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http://www.archive.org/details/workingofsteelanOOcolv 



THE WORKING OF STEEL 



ANNEALING, HEAT TREATING AND 

HARDENING OF CARBON 

AND ALLOY STEEL 



\&. 




VMe Qraw-J/ili Book (h 7n& 

PUBLISHERS OF BOOKS FOIL/ 

Coal Age v Electric Railway Journal 
Electrical World v Engineering News-Record 
American Machinist v Ingenien'a Internacional 
Engineering S Mining Journal ^ Power 
Chemical & Metallurgical Engineering 
Electrical Merchandising 




THE 

WORKING OF STEEL 



ANNEALING, HEAT TREATING 

AND 

HARDENING OF CARBON AND ALLOY STEEL 



BY 

FRED H. COLVIN 

Member American Society of Mechanical 1 Engineers and Franklin Institute; 

Editor of the American Machinist, Author of "Machine Shop 

Arithmetic," "Machine Shop Calculations," 

"American Machinists' Hand Book." 

AND 

K. A. JUTHE, M.E. 

Chief Engineer, American Metallurgical Corp. 

Member American Society Mechanical Engineers, American Society 

Testing Materials, Heat Treatment Association, Etc. 



First Edition 
First Impression 



McGRAW-HILL BOOK COMPANY, Inc. 

NEW YORK: 370 SEVENTH AVENUE 

LONDON: 6 & 8 BOUVERIE ST., E. C. 4 

1921 



CA 



copyright, 1921, by the 
McGraw-Hill Book Company, Inc. 



ai~i&7'i 



HUG 11 '2 



THE MAPLE PRESS YORK PA 



©CLA622418 




PREFACE 

The ever increasing uses of steel in all industries and the 
necessity of securing the best results with the material used, 
make a knowledge of the proper working of steel more im- 
portant than ever before. For it is not alone the quality of the 
steel itself or the alloys used in its composition, but the proper 
working or treatment of the steel wihch determines whether or 
not the best possible use has been made of it. 

With this in mind, the authors have drawn, not only from 
their own experience but from the best sources available, in- 
formation as to the most approved methods of working the 
various kinds of steel now in commercial use. These include 
low carbon, high carbon and alloy steels of various kinds, and 
from a variety of industries. The automotive field has done 
much to develop not only new alloys but efficient methods of 
working them and has been drawn on liberally so as to show 
the best practice. The practice in government arsenals on 
steels used in fire arms is also given. 

While not intended as a treatise on steel making or metal- 
lurgy in any sense, it has seemed best to include a little in- 
formation as to the making of different steels and to give 
considerable general information which it is believed will be 
helpful to those who desire to become familiar with the most 
modern methods of working steel. 

It is with the hope that this volume, which has endeavored 
to give due credit to all sources of information, may prove of 
value to its readers and through them to the industry at large. 

July, 1921 The Authors. 



CONTENTS 

Page 

Preface v 

Introduction ix 

Chapter 

I. Steel Making 1 

II. Composition and Properties of Steels 12 

III. Alloys and Their Effect upon Steel 24 

IV. Application of Liberty Engine Materials to the Auto- 

motive Industry 46 

V. The Forging of Steel 64 

VI. Annealing 75 

VII. Case-hardening or Surface-carburizing 79 

VIII. Heat Treatment of Steel 105 

IX. Hardening Carbon Steel for Tools 145 

X. High Speed Steel 165 

XL Furnaces 185 

XII. Pyrometry and Pyrometers 202 

Appendix 231 

Index 239 



INTRODUCTION 

THE A B C OF IRON AND STEEL 

In spite of all that has been written about iron and steel there 
are many hazy notions in the minds of many mechanics regarding 
them. It is not always clear as to just what makes the difference 
between iron and steel. We know that high-carbon steel makes 
a better cutting tool than low-carbon steel. And yet carbon 
alone does not make all the difference because we know that cast 
iron has more carbon than tool steel and yet it does not make a 
good cutting tool. 

Cast iron has from 3 to 5 per cent carbon, while good tool steel 
rarely has more than 1}^ per cent of carbon, yet one is soft and 
has a coarse grain, while the other has a fine grain and can be 
hardened by heating and dipping in water. The carbon in cast 
iron is what is called graphitic carbon, that is, it is in the form of 
graphite, which is almost pure carbon. The resemblance can be 
seen by noting how cast-iron borings blacken the hands just as 
does graphite, while steel turnings do not have the same effect. 
The difference is due to the fact that the carbon in steel is not 
in a graphitic form as well as because it is present in smaller 
quantities. 

In making steel in the old way the cast iron was melted and the 
carbon burnt out of it, the melted iron being stirred or "puddled, " 
which gave it the long grain or fibers similar to molasses candy 
which has been pulled. Then the iron was heated with material 
containing carbon until it absorbed the desired amount, which 
made it steel, just as case-hardening iron or steel adds carbon to 
the outer surface of the metal. The carbon absorbed by the iron 
does not take on a graphitic form, however, as in the case of cast 
iron. The carbon in cast iron makes it brittle instead of strong 
as in steel. 

A little study of malleable iron may help to understand the 
nature of steel and the way in which it differs from cast iron. In 
making malleable iron, the castings are heated in a furnace to 
from 1,700 to 2,100°F. and kept at this temperature from 48 to 
96 hr., both the heat and the time depending on the size of the 

ix 



X INTRODUCTION 

castings. This heat burns out most of the carbon making the 
metal more like wrought iron. The continued heat and the slow 
cooling in the furnace as it cools down, away from the air, robs it 
of most of its carbon. This same thing happens to some extent 
with tool steels when heated for annealing. The outer skin loses 
its carbon and must be removed before finishing and hardening, 
if a tool with a hard surface is desired. 

Malleable iron resembles wrought iron in that it is not brittle, 
that the castings can be bent or straightened, and that it can be 
welded if care is used. Borax and a little sand are used for the 
flux. Malleable iron, however, is not to be compared with 
wrought iron for strength, as it is not worked by rolling or ham- 
mering is in the case of wrought iron. The high and continued 
heat leaves the metal more or less porous, but still having some 
of the qualities of wrought iron. 



THE WORKING OF STEEL 

ANNEALING, HEAT TREATING AND HARDENING 

OF 

CARBON AND ALLOY STEEL 

CHAPTER I 

STEEL MAKING 

There are four processes used for the manufacture of steel. 
These are: The Bessemer, Open Hearth, Crucible and Electric 
Furnace Methods. 

BESSEMER PROCESS 

The bessemer process consists of melting iron in a cupola or 
special furnace for the purpose, and drawing it in sufficient 
amounts for charging the bessemer converter, and then in blowing 
a current of air through the charge from the bottom. 

This blast increases the temperature of the charge and all the 
foreign matter, excepting the oxide left by air passing through, 
is either burnt or blown out. 

When steel has reached its proper heat, the "medicine" 
(carbon, manganese or other elements wanted) is added, and the 
blast again applied to mix the charge thoroughly. 

A bessemer steel is necessarily high in impurities — particularly 
sulphur, phosphorous and oxide, left by the air blast. 

A bessemer converter is shown in Fig. 1, while Fig. 2 shows 
the details of its construction. This shows how the air blast is 
forced in from one side, through the trunnion, and up through 
the metal. Where the steel is melted the converter is tilted, or 
swung on its trunnions, until the molten steel can flow out of 
the top. 

OPEN HEARTH PROCESS 

The open hearth furnace consists of a basin-like structure 
with a basic or acid lining, which is charged with the iron to be 
converted. Over this, a strong current of air is blown, and a high 

1 



2 THE WORKING OF STEEL 

heat is produced. In this way it is claimed that the impurities 
are removed by combustion and by oxidation of the blast as they 
rise to the surface and the refined iron is ready to receive the 
charge of medicine and become thoroughly mixed by the con- 
tinued blast. 




\. typical Bessemer converter. 



The modern furnaces are so constructed that this blast can 
be controlled and reversed. It is claimed that this process does 
not impart so much oxygen to the steel as the bessemer process, 
when the blast is forced through the metal instead of over it. 

The details of a regenerative open hearth furnace are shown in 
Fig. 3. The steel is melted on the hearth by the heat of the mixed 



STEEL MAKING 3 

gas and air which passes over it. The diagram shows where and 
how both the gas and air come from and how they get from the 



If- 




Wmmm^m 
; § 1 

ll 1 1 111 

■ 1 1 1 H 




Fig. 2. — Action of Bessemer converter. 




Fig. 3. — Regenerative open hearth furnace. 



inlets to the chimney. The direction of flow is reversed about 
every 20 min. by changing the position of the dampers. 



THE WORKING OF STEEL 



CRUCIBLE STEEL 



Crucible steel is made by melting material in a clay crucible. 
These are generally located in rows flush with the floor. Each 
crucible contains a 95-lb. charge, which is composed of refined 
iron and the "medicine." This "medicine" covers carbon, and 
different other elements as per specifications called for on carbon 
or alloy steels. The crucibles are covered and sealed. 

The molten metal is poured into molds. When cool, the 
molds are removed, and the ingot remains. These ingots are 




Fig. 4. — Typical crucible furnace. 



then graded by first "topping," or breaking off a certain section 
of upper end to determine carbon content. They are then 
sent to a hammer shop, where they are thoroughly hammered. 
They are next cut into smaller sections called billets, and sent to 
the rolling mills to be rolled into bars. 

A typical crucible furnace is shown in Fig. 4, which also shows 
the ingot mold being filled from the crucible. 

THE ELECTRIC PROCESS 

The fourth method of manufacturing steel is by the electric 
furnace method. These furnaces are made rather long and nar- 



STEEL MAKING 5 

row, and 3 to 4 ft. deep. Generally, four electrodes, reaching 
from top to bottom, are placed in the furnace, and after charging 
5 to 10 tons of material, electric current is applied. Intense 
heat is generated by current passing from one electrode through 
the mass to the next electrode, melting the material thoroughly. 
It actually boils the molten metal, which is left in this state 
until material is thoroughly "killed," i.e., until such time as all 
impurities are burned out of the steel and, rising to the top, are 
thrown out as oxide. 

The superiority of electric melting, over other methods, is due 
to the fact that melting is done from the interior body of material 
and not from bottom or sides of furnace, giving a thorough, 
uniform material. 

During the process of " killing," tests are constantly taken 
from metal, which are analyzed for the purposes of checking up 
specifications. Some details of electric steel making follow: 

ELECTRIC STEEL MAKING 

Electric steel is made either by melting a cold charge and 
refining it in the electric furnace, known as "cold-melt electric 
steel," or by refining in the electric furnace the molten charge 
from the open hearth or bessemer or a combination of both. 
This latter method is applicable especially to furnaces of 10 tons 
capacity and upward, the cold-melt method not having proved 
successful to date in the large units. Figure 5 shows an electric 
furnace "slagging off" and Fig. 6 the pouring of ingots. 

The electric furnace, as known in this country, is a metal- 
lurgical instrument for the making of steel by means of electric 
arcs formed between electrodes or between electrodes and the 
metal bath. It consists essentially of a steel tank lined with 
refractory materials and fitted with working doors, spout and 
tilting arrangements for pouring and slagging off. Carbon or 
graphite electrodes of suitable section are inserted through the 
roof or sides and can be regulated. A high-tension electrical 
supply is brought into a transformer house adjoining the furnace 
and transformed down to about 100 volts for use at the electrodes. 

The heat generated by the electric arcs makes possible any 
desired temperature up to the fusion point of the best refractory 
materials. The temperature in the furnace is under the control 
of the operator and is changed as the refinement of the steel 
progresses. 



(i 



THE WORKING OF STEEL 



As an illustration of the furnace reactions that take place the 
following schedule is given, showing the various stages in the 







i % 



Fig. 5. — "Slagging off" 



?tric furnace. 



■£■» 4 - 



Fig. 6. — Pouring the ingots. 

making of a heat of electric steel. The steel to be made was a 
high-carbon chrome steel used for balls for ball bearings: 

6-Ton Heroult Furnace 
11:50 A.M.— Material charged: 

Boiler plate 5,980 lb. 

Stampings 5,991 lb. 

. 11,971 lb. 
Limestone 700 lb. 



STEEL MAKING 7 

12:29 P.M. — Completed charging (current switched on). 
3:20 P.M.— Charge melted down. 

Preliminary analysis under black slag. 
Analysis: 

C Si Su Ph Mn 

0.06 0.014 0.032 0.009 0.08 

Note the practical elimination of phosphorus. 
3:40 P.M. — The oxidizing (black) slag is now poured and skimmed off as 
clean as possible to prevent rephosphorizing and to permit of adding 
carburizing materials. For this purpose carbon is added in the form 
of powdered coke, ground electrodes or other forms of pure carbon. 

The deodorizing slag is now formed by additions of lime, coke 
and fluorspar (and for some analyses ferrosilicon) . The slag 
changes from black to white as the metallic oxides are reduced 
by these deoxidizing additions and the reduced metals return to 
the bath. A good finishing slag is creamy white, porous and 
viscous. After the slag becomes white, some time is necessary 
for the absorption of the sulphur in the bath by the slag. 

The white slag disintegrates to a powder when exposed to the 
atmosphere and has a pronounced odor of acetylene when wet. 

Further additions of recarburizing material are added as 
needed to meet the analysis. The further reactions are shown 
by the following : 

3:40 P.M. — Recarburizing material added: 
130 lb. ground electrodes. 
25 lb. ferrornanganese. 
Analysis 

C Si Su Ph Mn 

0.76 0.011 0.030 0.008 0.26 



To form white slag there 


was added: 






225 lb. lime. 








75 lb. powdered coke. 








55 lb. fluorspar. 








4:50 P.M.— 








Analysis : 








~C Si 


Su 


Ph 


Mn 


0.75 0.014 


0.012 


0.008 


0.28 



Note the reduction of the sulphur content. 

During the white-slag period the following alloying additions 
were made: 

500 lb. pig iron. 
80 lb. ferrosilicon. 

9 lb. ferrornanganese. 
146 lb. 6 per cent carbon ferrochrome. 



8 THE WORKING OF STEEL 

The furnace was rotated forward to an inclined position and 
the charge poured into the ladle, from which in turn it was 
poured into molds. 

5:40 P.M.— Heat poured. 
Analysis : 

C Si Su Ph Mn Cr 

0.97 0.25 0.014 0.013 0.33 0.70 

Ingot weight poured 94 . per cent 

Scull 2.7 per cent 

Loss 3.3 per cent 

Total current consumption for the heat, 4700 kw.-hr. or 710 kw.-hr. per 
ton. 

Electric steel, because of its density, should be cast in inverted 
molds with refractory hot tops to prevent any possibility of 
pipage in the body of the ingot. In the further processing of the 
ingot, whether in the rolling mill or "forge, special precautions 
should be taken in the heating, in the reduction of the metal and 
in the cooling. 

No attempt is made to compare the relative merits of open 
hearth and electric steel; results in service, day in and day out, 
have, however, thoroughly established the desirability of electric 
steel. Ten years of experience indicate that electric steel is 
equal to crucible steel and superior to open hearth. 

The rare purity of the heat derived from the electric arc, 
combined with definite control of the slag in a neutral atmosphere, 
explains in part the superiority of electric steel. Commenting 
on this recently Dr. H. M. Howe stated that "in the open hearth 
process you have such atmosphere and slag conditions as you 
can get, and in the electric you have such atmosphere and slag 
conditions as you desire. " 

Another type of electric furnace is shown in Figs. 7 and 8. 
This is the Ludlum furnace, the illustrations showing a 10-ton 
size. Figure 7 shows it in normal, or melting position, while in 
Fig. 8 it is tilted for pouring. In melting, the electrodes first rest 
on the charge of material in the furnace. After the current is 
turned on they eat their way through, nearly to the bottom. 
By this time there is a pool of molten metal beneath the electrode 
and the charge is melted from the bottom up so that the roof is 
not exposed to the high temperature radiating from the open arc. 
The electrodes in this furnace are of graphite, 9 in. in diameter 
and the current consumed is about 500 kw.-hr. per ton. 



STEEL MAKING 9 

One of the things which sometimes confuse regarding the 
contents of steel is the fact that the percentage of carbon and the 
other alloys are usually designated in different ways. Carbon 




Fig. 



-Ludlum electric fur 




Fig. 8. — The furnace tilted for pouring. 

is usually designated by " points" and the other alloys by per- 
centages. The point is one ten-thousandth while 1 per cent is 
one one-hundredth of the whole. In other words, "one hundred 



10 



THE WORKING OF STEEL 



point carbon" is 1 per cent. Twenty (20) point carbon, such 
as is used for carbonizing purposes is 0.2 per cent. Tool steel 
varies from one hundred to one hundred and fifty points carbon, 
or from 1 to 1.5 per cent. 

Nickel, chromium, etc., are always given in per cent as a 
35.0 per cent nickel, which means exactly what it says — 3>^ 
parts in 100. Bearing this difference in mind all confusion will 
be avoided. 

CRITICAL POINTS 

The heating or cooling of steel does not proceed uniformly as 
there seems to be a lagging or retardation at certain temperatures. 
These are called critical points or critical temperatures and are 
caused by physical changes in the steel whereby heat is liberated 



1553 
1535 
1515 
















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4 C 3/ 
























1475 
1155 

"5 H35 
h 

bo 

p 1195 
















































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i 


lc 2 " 


































































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1355 
1335 
1315 
1295 
1275 














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1235 
1215 
1195 












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Heating Curve Cooling Curve 

Fig. 9. — Critical point diagram. 

on cooling and is likewise absorbed in heating. According to 
Howe the changes occur at a lower temperature on cooling than 
on heating, unless the rates are infinitely slow. This is because 
of molecular inertia or lag. 

There are three principal critical points which are now usually 
designated as A h A 2 and A 3 , the first being the lowest. For 
the sake of distinguishing the different points, the heating or 
points of rising temperature, are designated asAc h Ac 2 and Ac 3 , 



STEEL MAKING 



11 



and the cooling points as Ar\, Ar% and Ar-s. While cooling 
through the lowest point there is a sufficient liberation of heat 
to show a glow in the dark and to actually raise the temperature 
to a slight degree. This is shown in Fig. 9, where the heating 
and cooling curves are marked so that decalescent and recalescent 
points can be seen. 

CLASSIFICATIONS OF STEEL 

Steel makers have no uniform classification for the various 
kinds of steel or steels used for different purposes. The following 
list shows the names used by some of the well-known makers: 



Air-hardening steel. 

Alloy steel 

Automobile steel 

Awl steel 

Axe and hatchet steel 

Band knife steel 

Band saw steel 

Butcher saw steel 

Chisel steel 

Chrome-nickel steel 

Chrome-vanadium steel 

Circular saw plates 

Coal augur steel 

Coal mining pick or cutter steel 

Coal wedge steel 

Cone steel 

Crucible cast steel 

Crucible machinery steel 

Cutlery steel 

Drawing die steel (Wortle) 

Drill rod steel 

Facing and welding steel 

Fork steel 

Gin saw steel 

Granite wedge steel 

Gun barrel steel 

Hack saw steel 



High-speed tool steel 

Hot-rolled sheet steel 

Lathe spindle steel 

Lawn mower knife steel 

Machine knife steel 

Magnet steel 

Mining drill steel 

Nail die shapes 

Nickel-chrome steel 

Paper knife steel 

Patent, bush or hammer steel 

Pick steel 

Pivot steel 

Plane bit steel 

Quarry steel 

Razor steel 

Roll turning steel 

Saw steel 

Scythe steel 

Shear knife steel 

Silico-manganese steel 

Spindle steel 

Spring steel 

Tool holder steel 

Vanadium tool steel 

Vanadium-chrome steel 

Wortle steel 



CHAPTER JI 

COMPOSITION AND PROPERTIES OF STEELS 

This deals with the compositions of steels used for the manu- 
facture of the various parts of intricate special machinery, 
especially airplane engines, requiring materials possessing 
unusually high tensile strength and shock-resisting qualities. A 
study of the many steel alloys in common use will enable the 
manufacturer to select from among their number a few brands 
embodying the particular qualities essential to his product, and 
by concentrating his attention upon them he may reduce the 
element of uncertainty and consequent hazard that must neces- 
sarily follow a wider range of selection. 

Most branches of the engineering trades are at one time or 
another faced with the necessity of reducing the weight of some 
piece of mechanism. This applies particularly to the manufac- 
ture of automobiles and airplanes and forms probably the chief 
reason for a thorough study of the nature and properties of the 
materials employed in the construction of such mechanisms. 

It is essential that the designer should have a full knowledge 
of the strength and durability of all the materials to be used, and 
it is important that those materials should be of a specified com- 
position and that the treatment should be checked by suitable 
tests in order that the results in actual practice shall correspond 
with the data on which the designer worked. 

Until about 1914, knowledge of the composition of aircraft 
steels and experience in their treatment was very limited; today 
there are so many brands of alloy steels requiring different treat- 
ment that great care must be exercised. As the hardening and 
tempering process is liable to error owing to the number of brands 
available, users are advised to choose as few types of steel as 
possible to cover their requirements. The treatment of the 
selected ones then quickly becomes familiar and the possibility of 
error is reduced. 

A range of about 10 steels will cover practically all require- 
ments. We give herewith the composition and properties of a 
range which may be chosen to advantage. 

12 



COMPOSITION AND PROPERTIES OF STEELS 13 

As variation in heat treatment is required with different steels 
in order to obtain the best results it is necessary to consider the 
mechanical properties along with the chemical composition. It is 
possible, however, particularly in the case of nickel-chrome steels, 
to obtain widely varying results with varied heat treatment. 

The following table has been compiled from actual tests made 
with a particular make of nickel-chrome oil-hardening steel and 
illustrates this point very well: 











R.A. 




O.H. 


T. 


Time 


T.S. 


Per cent 


B.N, 


825 


650 


30 


59 


57 


269 


S25 


600 


30 


64 


48 


286 


S25 


550 


30 


69 


42 


321 


825 


500 


30 


75 


43 


332 


825 


450 


30 


85 


42 


375 


825 


450 


20 


87 


49 


364 


825 


400 


30 


96 


38 


41S 


825 


350 


30 


104 


33 


430 


S25 ■ 


200 


15 


121 


38 


512 


825 


not 


tempered 


123 


34 


477 


825 


not 


tempered 


126 


21 


512 


800 


not 


tempered 


127 


27 


477 



O.H. = Temperature in degrees Centigrade at which sample was hard- 
ened in oil. 
T. = Temperature in degrees Centigrade at which sample was temp- 
ered. 
Time = Time in minutes for tempering. 
T.S. = Tensile strength in tons per square inch given by test piece. 
R.A. = Reduction of area registered during above test. 
B.N. = Brinell hardness number. 

The material which gave the above tests when treated in the 
manner indicated forms the basis of a most interesting met- 
allurgical study and is of exceptional value in aircraft work. It 
will be noticed that various degrees of hardness can be obtained, 
and this factor is of special utility in the manufacture of articles 
where distortion is a disadvantage and at the same time difficult 
to avoid. 

The articles are first rough-machined and then heat-treated to 
a Brinell hardness of 250 to 321. At this hardness the articles 
can be machined and we then have no distortion in the finished 
goods as there is no subsequent heat treatment. It will thus be 
seen that it is possible to obtain widely varying results from one 
brand of steel, and it might also be said that it is possible to obtain 



14 THE WORKING OF STEEL 

similar results from two steels of widely different chemical 
composition. 

It is advisable that the steel manufacturer should cooperate to 
a greater extent with the steel user to obtain a better understand- 
ing of the work which the finished article has to perform. Items 
subjected to different stresses require different materials and 
treatment, and in the case of resistance to wear it is well to bear in 
mind that a steel containing low proportions of nickel and 
chromium will resist wear better than a steel containing a high 
proportion of nickel and no chromium. 

It has become generally recognized that it is not only necessary 
to utilize materials of a sufficiently high yield point but the 
materials must also be of a nature suitable for resisting wear if 
the articles are subjected to abrasion and able to withstand 
shock if the articles are subjected to vibration. The advisability 
of putting samples of the materials through tests which bear 
some resemblance to the stresses which will be met in actual use 
is obvious, and in connection with airplane-engine manufacture 
this question has been given considerable attention. 

Perhaps the first decision to be reached in the manufacture of 
parts which are highly stressed is in relation to the composition 
of the materials employed. It will be understood that if the 
material should be of incorrect proportions satisfactory results 
can hardly be expected. 

It is expensive to introduce nickel, chromium, manganese and 
vanadium into mild steel, and unless the alloy thus produced is 
carefully watched its value may be destroyed as the result of 
incorrect proportions of carbon, sulphur and phosphorus. A full 
chemical analysis from time to time is necessary to preserve 
equality of product. 

In addition to the expense of manufacture, alloy steels require 
more careful treatment and a scientifically arranged system of 
checking temperatures is necessary if the results are to be relied 
upon. As the employment of these steels is necessary when we 
require an ultimate strength reaching to 130 tons per square inch 
the expense of materials and testing apparatus must be met. 

DIFFERENCE IN TREATMENT 

The alloys differ widely, and the treatment of these various 
alloy steels must be modified to suit each particular composition. 
When nickel is added to plain carbon steel the skin of the hard- 



COMPOSITION AND PROPERTIES OF STEELS 15 

ened material is harder and the depth to which the quenching 
effect penetrates is greater. Chromium and tungsten added to 
plain carbon steel enable a more highly finished surface to be 
obtained when machining, and a finer grain is produced in the 
metal, but these elements do not appear to materially influence 
the hardness or the depth of case of the hardened material. 
Chrome-vanadium steels do not appear to have given quite as 
successful results as nickel-chrome steels, but for certain purposes 
they are preferable. 

Nickel is perhaps the most valuable element to the met- 
allurgist, and b}? - simply normalizing a bar of nickel steel to the 
same tensile strength as a sample of medium-carbon steel a 
comparison of the results readily establishes the superiority of 
the alloy steel. Increased elasticity is obtained and the impact- 
test figures are considerably improved, so that in cases where 
elasticitjr and shock-resisting qualities are required nickel steel is 
preferable, providing the carbon content is not excessive in 
proportion to the nickel. If the carbon content is not within 
the limits that will be specified later, the probability is that the 
article would fracture under a lighter load than would plain 
carbon steel. 

Bearing in mind the influence of these alloys when introduced 
into steel we can proceed to inquire into the composition of the 
materials, and it must be noted that it is necessary to maintain 
the proportions of the elements within certain limits in relation 
to each other. 

CARBON STEEL 

The use of plain carbon steel in aircraft work is quite restricted, 
as we generally require material able to withstand higher stresses; 
but it can be used for certain parts which are not subjected to 
great shock or wear, such as tachometer gear. It is then possible 
to use steel suitable for automatic machinery, and material of 
the following specification will be found to give satisfactory 
results : 

Per cent 

Carbon, not greater than 0. 25 

Manganese, not greater than 0.85 

Silicon, not greater than 0.20 

Phosphorus, not greater than. 0.06 

Sulphur, not greater than 0. 06 

Should it be required to use a slightly higher tensile steel the 
following proportions will be found satisfactory, but machining 



16 THE WORKING OF STEEL 

is more difficult and the tools will require more frequent 

attention: 

Per cent 

Carbon, not greater than . . 0.40 

Manganese, not greater than 1 .00 

Silicon, not greater than . 20 

Phosphorus, not greater than 0.06 

Sulphur, not greater than . 06 

Neither of the above steels are suitable for case-hardening, 
but as they can be obtained in bright drawn bars the advantages 
of their use in all possible instances are obvious. Although case- 
hardening nickel steel has in many cases taken the place of case- 
hardening mild steel the latter is still used to a great extent in the 
manufacture of valve tappets, engine-timing gears, camshafts, 
gudgeon pins, etc. Parts made from this material present a 
good resistance to wear, and two qualities, low and medium car- 
bon, may be used with advantage. The low carbon will give a 
minimum of 23 tons breakiDg strength when normalized at 900 
to 920°C. and the composition as follows: 

Per cent 

Carbon 0.10 

Silicon 0.18 

Manganese 0.60 

Sulphur 0. 04 

Phosphorus . 04 

When this material is normalized as above, the physical tests 
should be as follows: 

Breaking strength 23 to 28 tons per square inch 

Yield ratio Not less than 50 per cent 

Elongation Not less than 30 per cent 

Reduction of area Not less than 50 per cent 

Brinell hardness 92 to 112 

This material, if well made, will be found to case-harden well 
and uniformly, but it is frequently necessary to employ a similar 
steel with slightly improved breaking strength, although there is 
a tendency for the elongation to diminish. 

Another quality of case-hardening mild steel can be specified 
as follows: 

Per cent 

Carbon 0.15 

Silicon 0.18 

Manganese 0.75 

Sulphur 0. 06 

Phosphorus. . 06 



COMPOSITION AND PROPERTIES OF STEELS 1 7 

It will be noticed that higher proportions of sulphur and 
manganese are permissible in this instance. When the above 
material is normalized at 890 to 920°C. the following tests should 
be obtained: 

Tensile breaking strength 25 to 33 tons per square inch 

Yield ratio Not less than 50 per cent 

Elongation Not less than 25 per cent 

Reduction in area Not less than 50 per cent 

Brinell hardness 103 to 143 

The normalizing temperatures given are within 50°C. above 
the critical temperature in each case. 

The carburizing should take place at 900°C, the length of 
time depending upon the depth of case required, and the articles 
should then be allowed to cool down in the compound. In 
order to refine the structure of the case the articles should be 
heated to about 870°C, and either allowed to cool in the air or 
be quenched in water. Finally they should be reheated to 
780°C, and quenched in water to harden the case. 

With certain makes of steel not conforming correctly to the 
above specifications it may be necessary to depart very slightly 
from the above temperatures, but the most suitable conditions 
can readily be ascertained by trial and a little advice from the 
steel maker. 

There are many instances where it is necessary to have some 
knowledge of the properties of the core of case-hardened articles, 
and this can be obtained by putting test pieces through the same 
heat treatment and at the same time as the parts being manu- 
factured, and turning off the case to the depth to which the 
carbon has penetrated. It will generally be found that by the 
refining influence of the heat treatment the yield point and 
the breaking strength are improved and that the elongation and 
reduction of area are reduced. 

In some recent tests in connection with the last-named material 
the tests on the material as rolled and after the hardening 
treatment were: 

As rolled After treatment 

Breaking strength 31 tons 36 tons 

Yield point 21 tons 25 tons 

Elongation 28 per cent 23 per cent 

Reduction of area 58 per cent 51 per cent 

These figures are of value, as it must be realized that we cannot 
rely on the case to withstand shocks and our calculations must 



18 THE WORKING OF STEEL 

consider the extent to which the material may be loaded, based 
on the strength of the core only. 

Should circumstances arise where it is necessary to employ 
material of higher ultimate strength and better surf ace- wearing 
qualities than the case-hardening carbon steels detailed above, 
use can be made of case-hardening nickel steels, and here it is 
necessary to exercise greater care in manufacture and heat 
treatment. 

LOW-NICKEL STEEL 

A good low-nickel alloy steel can be made up as follows: 

Per cent 

Carbon 0.13 

Silicon 0.25 

Manganese . 45 

Sulphur 0.04 

Phosphorus . 04 

Nickel - 2.00 

The phosphorus content must be carefully checked, for if 
excessive it will cause cold shortness, and attempts to straighten 
parts which may become distorted in hardening will result in 
fracture. Excess of sulphur produces hot shortness. 

This material when normalized at 850 to 900°C. should give 
the following results: 

Tensile breaking strength 25 to 35 tons per square inch 

Yield ratio Not less than 55 per cent 

Elongation Not less than 30 per cent 

Reduction of area Not less than 55 per cent 

Brinell hardness 103 to 153 

A step higher in tensile breaking strength and yield ratio can 
be obtained with an alloy steel containing a larger proportion 
of nickel and the elongation will remain about the same. 

A chemical analysis of such a steel should show the results 
given below, and the necessity for maintaining a low proportion 
of the injurious elements renders the manufacture of this steel 
somewhat difficult and consequently expensive: 

Per cent 

Carbon 0.15 

Silicon 0.18 

Sulphur 0.04 

Phosphorus . 04 

Manganese 0.35 

Nickel 5.00 

The case-hardening nickel steels given above are suitable for 
articles where a good, hard wearing surface is necessary, but 



COMPOSITION AND PROPERTIES OF STEELS 19 

when quenching to harden the case it is necessary to reheat to 
a somewhat lower temperature than is the case with carbon 
steels. When it is decided which brand of material to use it is 
advisable to carry out a series of tests to ascertain the most 
suitable temperature. 

Occasionally it is necessary to manufacture articles where 
good wearing qualities are required, but the parts are so thin 
that a hard case would be disastrous as there would be no core 
left. In such instances an alloy steel containing about 3 per cent 
nickel, 0.30 per cent carbon and about 0.70 per cent manganese 
will be found of great value as it is thus possible to obtain 45 
tons per square inch ultimate stress and a Brinell hardness of 
about 200. 

The materials which have probably been of greatest value to 
the automobile manufacturer engaged on airplane-engine work 
are probably the alloy steels containing nickel and chromium 
in their composition. These alloys can be so constructed that 
they can first be hardened and then tempered to give almost 
any degree of hardness between 250 and 500 Brinell, and it is not 
a difficult matter to bring the hardness to about 320 Brinell. 
Up to this figure the material can be machined and the parts 
will stand a great deal of shock and wear, but should the hardness 
be greater the probability is that the further machining would be 
impossible. 

It must not be concluded from the above remarks that the 
Brinell-hardness numeral can be taken as a general guide to 
the machining properties of materials, but in comparing two 
samples of the same steel it can be taken as a rough indication. 
When comparing different alloys it is quite possible that one 
steel can easily be cut by another which registers lower on 
Brinell test. The addition of nickel in excess of 1.5 per cent 
increases the toughness and difficulty in machining. 

A high-tensile nickel-chrome steel, suitable for tempering to 
various degrees of hardness can be built up as follows: 

Per cent 

Carbon 0.20 to 0.30 

Silicon Not over . 30 

Manganese . 35 to . 60 

Sulphur Not over 0. 04 

Phosphorus Not over 0. 04 

Nickel 2 . 75 to 3 . 50 

Chromium . 45 to . 75 



20 



THE WORKING OF STEEL 



If the above material be heated up to 820°C, quenched in 
whale oil and then tempered at 600°C. the test results should 
be approximately: 

Tensile breaking strength. : Not less than 45 tons per square inch 

Yield ratio Not less than 75 per cent 

Elongation Not less than 15 per cent 

Reduction of area. ... Not less than 50 per cent 

Brinell-hardness number 179 



•- 50 



cO 4.0 

<4- 



36 



































































































Q 


ra f 


h-r 


» 




























































































































































































.B 






























































































Qr 


01 Pi' 


l - E 








































































^_ 










1 







































































































150 200 250 300 350 400 45C 

Brinell Hardness Mumber 

Fig. 10.— Relation of Brinell hardness to tensile strength. 



When using this material for a high-tensile strain and a 
hardness of about 320 Brinell, as previously suggested, it is an 
advantage to rough out the parts before heat-treating so that 
very little metal is left for removing in the hard state. 

In connection with hardness and ultimate strength we often 
find attempts made to establish a law in which the two qualities 



COMPOSITION AND PROPERTIES OF STEELS 21 

are related. It is not correct to look upon the Brinell-hardness 
test as a measure of tensile strength when comparing materials 
of different composition, but when comparing the same brand 
of material treated to different degrees of hardness there is 
reasonably close connection between that hardness and the 
ultimate strength of the material in the same state. 

Some elaborate tests were made to ascertain this relation 
in the case of an alloy steel containing a moderate proportion 
of nickel and chromium, and by plotting the results of a Brinell 
test and tensile test on various heat-treated samples the chart 
shown in Fig. 10 was prepared. For that particular quality of 
material it was found possible to ascertain the tensile strength 
with a reasonable degree of accuracy after simply measuring the 
diameter of the impression left by a 10-mm. ball under a pressure 
of 3,000 kg. on the Brinell machine. 

It is simply necessary to locate on axis OA the position 
indicating the impression diameter in millimeters, and from 
that point travel horizontally to the curve in graph D, then 
vertically across axis OB to the curve in graph E and by traveling 
horizontally to axis OC we obtain the approximate tensile 
strength. 

SOME OF THE NAMES USED 

Steel makers and metallurgists use names which are not so 
familiar to steel users. Among these and most commonly used 
are "ferrite," "cementite" and "pearlite." Ferrite, according 
to Howe, is now employed to designate that part of iron or steel 
containing no carbide (or only a trace) in solid solution. Cemen- 
tite is the mixture of iron and carbon in the proportion of 93.4 
per cent iron and 6.6 per cent carbon. It is also known as a 
carbide of iron and has the symbol of Fe 3 C, which means that 
it is composed of 3 atoms of iron and 1 atom of carbon. 

Pearlite contains approximately 0.9 per cent of carbon and 
is found in inter-stratified layers or in bands of cementite and 
ferrite. It is considered as a separate constituent of steel and 
is called pearlite on account of its having the appearance of 
mother of pearl when examined under a microscope. Steel of 
this mixture forms a special class and is known as "eutectic" 
steel while steels containing less than this proportion of carbon 
(0.9 per cent) are called " hypo-eutectic steels." These steels 
however contain certain known amounts of pearlite and of free 
or excess ferrite. 



22 THE WORKING OF STEEL 

Steels are divided according to their carbon content into three 
classes: hypo-eutectoid, below 0.89 per cent carbon; eutectoid, 
at 0.89 per cent; and hyper-eutectoid above 0.89 per cent. The 
hypo-eutectic class will cover most of the airplane steels. The 
medium-carbon steel is a good illustration. 

This material is generally in an annealed condition to start 
with, or a mixture of ferrite and pearlite. As heat is applied 
and the steel passes the A 3 point, the constituents go into a 
solid solution consisting of iron carbide, cementite or a double 
carbide of iron and the special element (Cr, Va) in gamma iron. 
If this is quenched in salt water or other abrupt medium, it is 
called austenite, but if quenched in oil, probably martensite, 
which is a more stable form resulting from the austenite giving 
way along its cleavage planes. On heating or drawing marten- 
site, there is a slight precipitation of ferrite or beta iron. This 
mixture consisting of beta iron and a solid solution of carbide 
in gamma iron is called troosite which becomes sorbite on further 
drawing or on a further precipitation of beta iron. At the Ac% 
point the beta iron is converted into alpha iron and on the 
drawing being continued the gamma solution approaches the 
eutectic until at the Ac x point it is converted into pearlite. The 
mixture now consists of ferrite and pearlite. 

Annealing. — The object of annealing is to relieve strains and 
to soften the structure or make it normal. It consists in raising 
the steel to a temperature above the Ac% point and holding it 
a sufficient time to get a complete solid solution. Then allowing 
it to cool slowly in the furnace in order that all transformation 
.may be completed — austenite, martensite, troosite, sorbite and 
ending with a mixture of ferrite and pearlite. This is a furnace 
or soft anneal. 

Most annealing or better "normalizing" is done by merely 
heating past the Ac% point and then cooling in air. This gives 
a mixture of ferrite and sorbite instead of ferrite and pearlite 
as results in furnace cooling. If a fine structure is wanted 
coincidentally in a good soft material, quench at above the Acz 
point and draw at just below the Ac x point. 

Quenching. — -Materials are quenched in order to get maximum 
hardness and grain refinement. It consists in heating the steel 
past its Ac% point and quenching in oil or water. This retains 
it in its austenitic and martensitic condition which is very hard 
and fine. 



COMPOSITION AND PROPERTIES OF STEELS 23 

Drawing. — Drawing consists in heating to some point below 
Aci and cooling in air or oil. This is a softening or toughening 
process in which ferrite is liberated varying with the increase 
of draw. Practically all of these steels on being drawn are 
sorbitic. 

Grain Size. — Care should be exercised in not passing the 
upper critical too far, as the grain size grows accordingly and 
there is danger of overheating. 

Overheating. — This causes a very coarse structure but it can 
be restored by merely heating to a little above the critical (upper) 
point and quenching. Overheating should not be confounded 
with burning. 

Burning. — Burnt steel is brittle and its fracture is coarse 
and shiny. -Material that has been burnt is of no value in this 
work. 

Test Specimens. — All specimens that are heat-treated for 
test purposes are carefully machined to the required shape and 
size, then treated in electric or oil furnaces. Much attention 
should be paid to the machining of specimens, as an extra deep 
cut will spoil the test. This often occurs near the shoulder. The 
data from a poor specimen are of no value. 



CHAPTER III 

ALLOYS AND THEIR EFFECT UPON STEEL 

In view of the fact that alloy steels are coming into a great 
deal of prominence, it would be well for the users of these steels 
to fully appreciate the effects of the alloys upon the various 
grades of steel. We have endeavored to summarize the effect 
of these alloys so that the users can appreciate their effect, 
without having to study a metallurgical treatise and then, 
perhaps, not get the crux of the matter. 

NICKEL 

Nickel may be considered as the toughest among the non-rare 
alloys now used in steel manufacture. Originally nickel was 
added to give increased strength and toughness over that obtained 
with the ordinary rolled structural steel and little attempt was 
made to utilize its great possibilities so far as heat treatment 
was concerned. 

The difficulties experienced have been a tendency towards 
laminated structure during manufacture and great liability to 
seam, both arising from a non-homogeneous melting. When 
extra care is exercised in the manufacture, particularly in the 
melting and rolling, many of these difficulties can be overcome. 

The electric steel furnace, of modern construction, is a very 
important step forward in the melting of nickel steel; neither the 
crucible process nor basic or acid open hearth furnaces give such 
good results. It is also necessary that small ingots be made so 
as to cut out piping. 

Great care must be exercised in reheating the billet for rolling 
so that the steel is correctly soaked. The rolling must not be 
forced; too big reduction per pass should not be indulged in, as 
this sets up a tendency towards seams. 

Nickel steel has remarkably good mechanical qualities when 
suitably heat-treated, and it is preeminently adapted for case- 
hardening. It is not difficult to machine low-nickel steel, 
consequently it is in great favor where easy machining properties 
are of importance. 

24 



ALLOYS AND THEIR EFFECT UPON STEEL 25 

Nickel influences the strength and ductility of steel by being 
dissolved directly in the iron or ferrite; in this respect differing 
from chromium, tungsten and vanadium. The addition of each 
1 per cent nickel up to 5 per cent will cause an approximate 
increase of from 4,000 to 6,000 lb. per square inch in the tensile 
strength and elastic limit over the corresponding steel and without 
any decrease in ductility. The static strength of nickel steel 
is affected to some degree by the percentage of carbon; for 
instance, steel with 0.25 per cent carbon and 3.5 per cent nickel 
has a tensile strength, in its normal state, equal to a straight 
carbon steel of 0.5 per cent with a proportionately greater 
elastic limit and retaining all the advantages of the ductility of 
the lower carbon. 

To bring out the full qualities of nickel it must be heat-treated, 
otherwise there is no object in using nickel as an alloy with carbon 
steel as the additional cost is not justified by increased strength. 

Nickel has a peculiar effect upon the critical ranges of steel, 
the critical range being lowered by the percentage of nickel; in 
this respect it is similiar to carbon only more marked. Generally 
speaking, nickel steel requires a lower heat-treating temperature 
than chrome steel or tungsten steel, being very similar to manga- 
nese in this respect. 

Nickel can be alloyed with steel in various percentages, each 
percentage having a very definite effect on the microstructure. 
For instance, a steel with 0.2 per cent carbon and 2 per cent nickel 
has a pearlitic structure but the grain is much finer than if the 
straight carbon were used. With the same carbon content and 
say 5 per cent nickel, the structure would still be pearlitic, but 
much finer and denser, therefore capable of withstanding shock, 
and having greater dynamic strength. With about 0.2 per cent 
carbon and 8 per cent nickel, the steel is nearing the stage between 
pearlite and martensite, and the structure is extremely fine, the 
Ferrite and pearlite having a tendency to orientiate, as seen in a 
purely martensite structure. Steel with 0.2 per cent carbon and 
15 per cent nickel is entirely martensite. Higher percentages of 
nickel change the martensite structure to austenite, the steel then 
being non-magnetic. The higher percentages, that is 30 to 35 
per cent nickel, are used for valve seats, valve heads, and valve 
stems, as the alloy is a poor conductor of heat and is particularly 
free from any tendency towards corrosion or pitting from the 
action of waste gases of the internal-combustion engine. 



4 



26 THE WORKING OF STEEL 

To obtain the full effect of nickel as an alloy, it is essential 
that the correct percentage of carbon be used. High nickel and 
low carbon will not be more efficient than lower nickel and higher 
carbon, but the cost will be much greater. Generally speaking, 
heat-treated nickel alloy steels are about two to three times 
stronger than the same steel annealed. This point is very im- 
portant as many instances have been found where nickel steel 
is incorrectly used, being employed when in the annealed or 
normal state. 

CHROMIUM 

Chromium when alloyed with steel, has the characteristic 
function of opposing the disintegration and reconstruction of 
cementite. This is demonstrated by the changes in the critical 
ranges of this alloy steel taking place slowly; in other words, it 
has a tendency to raise the Ac range (decalescent points) and 
lower the Ar range (recalescent points). Chromium steels are 
therefore capable of great hardness, due to the rapid cooling 
being able to retard the decomposition of the austenite. 

The great hardness of chromium steels is also due to the forma- 
tion of double carbides of chromium and iron. This condition 
is not removed when the steel is slightly tempered or drawn. 
This additional hardness is also obtained without causing undue 
brittleness such as would be obtained by any increase of carbon. 
The degree of hardness of the lower-chrome steels is dependent 
upon the carbon content, as chromium alone will not harden iron. 

The toughness so noticeable in this steel is the result of the 
fineness of structure; in this instance, the action is similar to that 
of nickel, and the tensile strength and elastic limit is therefore 
increased without any loss of ductility. We then have the 
desirable condition of tough hardness, making chrome steels 
extremely valuable for all purposes requiring great resistance to 
wear, and in higher-chrome contents resistance to corrosion. 
All chromium-alloy steels offer great resistance to corrosion and 
erosion. In view of this, it is surprising that chromium steels 
are not more largely used for structural steel work and for all 
purposes where the steel has to withstand the corroding action of 
air and liquids. Bridges, ships, steel building, etc., would offer 
greater resistance to deterioration through rust if the chromium- 
alloy steels were employed. 

Prolonged heating and high temperatures have a very bad 
effect upon chromium steels. In this respect they differ from 



ALLOYS AND THEIR EFFECT UPON STEEL 27 

nickel steels, which are not so affected by prolonged heating, but 
chromium steels will" stand higher temperatures than nickel 
steels when the period is short. 

Chromium steels, due to their admirable property of increased 
hardness, without the loss of ductility, make very excellent 
chisels and impact tools of all types, although for die blocks they 
do not give such good results as can be obtained from other 
alloy combinations. 

For ball bearing steels, where intense hardness with great 
toughness and ready recovery from temporary deflection is re- 
quired, chromium as an alloy offers the best solution. 

Two per cent chromium steels, due to their very hard tough 
surface, are largely used for armor-piercing projectiles, cold 
rolls, crushers, drawing dies, etc. 

The normal structure of chromium steels, with a very low car- 
bon content is roughly pearlitic up to 7 per cent, and martensitic 
from 8 to 20 per cent; therefore, the greatest application is in the 
pearlitic zone or the lower percentages. 

NICKEL-CHROMIUM 

A combination of the characteristics of nickel and the char- 
acteristics of chromium, as described, should obviously give a 
very excellent steel as the nickel particularly affects the ferrite 
of the steel and the chromium the carbon. From this combina- 
tion, we are able to get a very strong ferrite matrix and a very 
hard tough cementite. The strength of a strictly pearlitic steel 
over a pure iron is due to the pearlitic being a layer arrangement 
of cementite running parallel to that of a pure iron layer in each 
individual grain. The ferrite i.e., the iron is increased in strength 
by the resistance offered by the cementite which is of the staple 
iron carbon combination or carbide known as Fe3c. The cemen- 
tite, although adding to the tensile strength, is very brittle and 
the strength of the pearlite is the combination of the ferrite and 
cementite. In the event of the cementite being strengthened, as 
in the case of strictly chromium steels, an increased tensile 
strength is readily obtained without loss of ductility .and if the 
ferrite is strengthened then the tensile strength and ductility 
of the metal is still further improved. 

Nickel-chromium alloy represents one of the best combinations 
available at the present time. The nickel intensifies the physical 
characteristics of the chromium and the chromium has a similar 
effect on the nickel. 



23 the Working of sVeeL 

For case-hardening, nickel-chromium steels seem to give very 
excellent results. The carbon is very rapidly taken up in this 
combination, and for that reason is rather preferable to the 
straight nickel steel. 

With the mutually intensifying action of chromium and nickel 
there is a most suitable ratio or these two alio; s, nd it has been 
found that roughly 2^ parts of nickel to about 1 part of chro- 
mium gives the best results. Therefore, we have the standard 
types of 3.5 per cent nickel with 1.5 per cent chromium to 1.5 
per cent nickel with 0.6 per cent chromium and the various 
intermediary types. This ratio, however, does not give the whole 
story of nickel-chromium combinations, and many surprising 
results have been obtained with these alloys when other percen- 
tage combinations have been employed. 

VANADIUM 

Vanadium has a very marked effect upon alloy steels rich in 
chromium, carbon, or manganese. Vanadium itself, when 
combined with steel very low in carbon, is not so noticeably 
beneficial as the same carbon steel higher in manganese, but if a 
small quantity of chromium is added, then the vanadium has a 
very marked dynamic effect. Therefore, it would seem that 
vanadium has the effect of intensifying the action of chromium 
and manganese, or that vanadium is intensified by the action of 
chromium or manganese. 

Vanadium has the peculiar property of readily combining 
with ferrite, also the carbon forming carbides and is to be found 
in solid solution in the ferrite. The ductility of carbon-vanadium 
steels is therefore increased, likewise the ductility of chrome- 
vanadium steels. 

The full effect of vanadium is not felt unless the temperatures, 
to which the steel is heated for hardening, are raised considerably. 
It is therefore necessary that a certain amount of soaking takes 
place, so as to get the necessary equalization. This is true of all 
cementitic compounds, of which vanadium is one. 

Chrome-vanadium steels also have a tendency for greater 
depth of hardening and anti-fatigue properties than can be 
obtained from straight chromium steels. It would appear that 
the intensification of the chrome and manganese in the alloy 
steel accounts for this peculiar phenomenon. 

Vanadium is also a very excellent scavenger for either remov- 



ALLOYS AND THEIR EFFECT UPON STEEL 29 

ing the harmful gases, or causing them to enter into solution with 
the metal in such a way as to largely obviate their harmful effects. 
Chrome-vanadium steels have been claimed, by many steel 
manufacturers and users, to be preferable to nickel-chrome 
steels. While not wishing to pass judgment on this, it should 
be borne in mind that the chrome-vanadium steel, which is 
tested, is generally compared with a very low nickel-chromium 
alloy steel (the price factor entering into the situation) , but 
equally good results can be obtained by nickel-chromium steels 
of suitable analysis. 

Where price is the leading factor, there are many cases where 
a stronger steel can be obtained from the chrome and vanadium 
than the nickel-chrome. It will be safe to say that each of 
these two systems of alloys have their own particular fields and 
chrome-vanadium steel should not be regarded as the sole solu- 
tion for all problems, neither should nickel-chromium. 

MANGANESE 

Manganese adds considerably to the tensile strength of steel, 
but this is dependent on the carbon content. High carbon ma- 
terially adds to the brittleness, whereas low-carbon, pearlitic- 
manganese steels are very tough and ductile and are not at all 
brittle, providing the heat-treating is correct. Manganese steel 
is very susceptible to high temperatures and prolonged heating. 

Low-carbon pearlitic-manganese steel is a very efficient steel, 
but its efficiency is entirety dependent on the temperature to 
which it is heated for hardening, or the temperature used for 
annealing. Low-carbon pearlitic-manganese steel made in the 
electric furnace seems to be more efficient than the same chemical 
analysis steel made by either the open hearth or crucible process. 
No reason has as yet been assigned for this peculiar phenomenon, 
but it is believed that the removal of the harmful gases, particu- 
larly oxygen and nitrogen, is responsible. 

Manganese when added to steel has the effect of lowering the 
critical range ; 1 per cent manganese will lower the upper critical 
point 60°F. The action of manganese is very similar to that of 
nickel in this respect, only twice as powerful. As an instance, 
1 per cent nickel would have the effect of lowering the upper 
critical range from 25 to 30°F. 

Low-carbon pearlitic-manganese steel, heat-treated, will give 
dynamic strength which cannot be equalled by low-priced and 



30 THE WORKING OF STEEL 

necessarily low-content nickel steels. In many instances, it is 
preferable to use high-grade manganese steel, rather than low- 
content nickel steel. 

High-manganese steels or austenite manganese steels are used 
for a variety of purposes where great resistance to abrasion is 
required, the percentage of manganese being from 11 to 14 per 
cent, and carbon 1 to 1.5 per cent. This steel is practically 
valueless unless heat-treated; that is, heated to about yellow 
red and quenched in ice water. The structure is then austenite 
and the air-cooled structure of this steel is martensite. Therefore 
this steel has to be heated and very rapidly cooled to obtain the 
ductile austenite structure. 

Manganese between 2 and 7 per cent is a very brittle material 
when the carbon is about 1 per cent or higher and is, therefore, 
quite valueless. Below 2 per cent manganese steel low in carbon 
is very ductile and tough steel. 

The high-content manganese steels are known as the "Had- 
field manganese steels," having been developed by Sir Robert 
Hadfield. Small additions of chrome up to 1 per cent increase 
the elastic limit of low-carbon pearlitic-manganese steels without 
affecting the steel in its resistance to shock, but materially 
decrease the percentage of elongation. 

Vanadium added to low-carbon pearlitic manganese steel has 
a very marked effect, increasing greatly the dynamic strength 
and changing slightly the susceptibility of this steel to heat 
treatments, giving a greater margin for the hardening tempera- 
ture. Manganese steel with added vanadium is most efficient 
when heat-treated. 

TUNGSTEN 

Tungsten, as an alloy in steel, has been known and used for a 
long time. The celebrated and ancient damascus steel being a 
form of tungsten-alloy steel. Tungsten and its effects, however, 
did not become generally realized until Robert Mushet experi- 
mented and developed his famous mushet steel and the many 
improvement made since that date go to prove how little 
Mushet himself understood the peculiar effects of tungsten as 
an alloy. 

Tungsten acts on steel in a similar manner to carbon, that is, it 
increases its hardness, but is much less effective than carbon in 
this respect. If the percentage of tungsten and manganese is 



ALLOYS AND THEIR EFFECT UPON STEEL 31 

high, the steel can be hardened by cooling in the air. This 
effect is directly opposite to that of carbon. It was this com- 
bination that Mushet used in his well-known steel. 

The principal use of tungsten is in high-speed tool steel, but 
here a high percentage of manganese is distinctly detrimental, 
making the steel liable to fire crack, very brittle, and weak in 
the body, less easily forged and annealed. Manganese should 
be kept low and a high percentage of chromium steel used instead. 

The tungsten-chromium steels, when hardened, retain their 
hardness, even when heated to a dark cherry red by the friction 
of the cutting or the heat arising from the chips. This charac- 
teristic led to the term "red hardness" being applied to this 
class of steel, and it is this property that is responsible for the 
increase of cutting speeds in the tungsten-chrome alloy, that is 
high-speed steel. 

Tungsten when added to steel up to 6 per cent does not have 
the property of red hardness any more than carbon tool steel, 
providing the manganese or chromium is low. Tungsten has a 
rapidly increasing cutting efficiency up to 13 per cent, thereafter 
falling until 14 per cent, then increasingly efficient until 18 per 
cent or more is used. 

If chromium is alloyed with tungsten, then a very definite red- 
hard effect is noticed with a great increase of cutting efficiency. 
The maximum red-hard cutting efficiency of the tungsten, chrome 
steel seems to be a definite chemical analysis ratio. But there 
are various mechanical and other reasons why this ratio is not 
used for high-speed steel, as high-chromium content steel is very 
easily spoiled by the high heats necessary in its heat treatment. 

Very little is known of the actual function of tungsten, al- 
though a vast amount of experimental work has been done. It 
is possible that when the effect of tungsten with iron carbon 
alloys is better known, a greater improvement can be expected 
from these steels. Tungsten has been tried and is still used by 
some steel manufacturers for making punches, chisels, and other 
impact tools. It has also been used for springs, and has given 
very good results, although other less expensive alloys give 
equally good results, and are in some instances, better. 

Tungsten is largely used in permanent magnets. In this, 
its action is not well understood. In fact, the reason why steel 
becomes a permanent magnet is not at all understood. Theories 
have been evolved, but all are open to serious questioning. The 



32 THE WORKING OF STEEL 

principal effect of tungsten, as conceded by leading authorities, 
is that it distinctly retards separation of the iron-carbon solution, 
removing the lowest recalescent point down to atmospheric 
temperature. 

A peculiar property of tungsten, when used in the iron-carbon 
alloys, is that if a temperature of 1,750°F. is not exceeded, it 
does not interfere with the carbide change, nor affect the tempera- 
tures of the recalescent points. But when the hardening tem- 
perature is raised above 1,850°F., a most remarkable effect is 
conveyed upon the falling transformation points, prevent- 
ing their formation entirely, down to about the atmospheric 
temperature. 

The lowering of the carbide change, which is produced by 
heating tungsten steels to over 1,850°F., is the real cause of 
the red-hard properties of these alloys, is not understood, and 
there is no direct evidence to show what actually happens at 
these high temperatures. 

There is every reason to believe that when the tungstide 
Fe2W is present, it gradually goes into solution as the tempera- 
ture is raised above 1,550°F., the amount of compound present 
being higher as the tungsten is increased. When completely in 
solution, the temperature of the carbide change (recalescent 
point) is lowered on cooling. It is quite an open question, how- 
ever, whether this lowering is entirely due to the Fe2W in solution, 
or whether some other chemical change also occurs. 

At a temperature above 1,850°F., there may be chemical 
reactions between the iron and tungsten carbide, which give a 
new compound, resulting in the disappearance of the critical 
point of the falling temperature 1,300°F., and the appearance of 
another point at a lower temperature. Other combinations, 
in which there should be no free tungstide of iron, give the same 
lowering of the carbide change after heating to high tempera- 
tures; therefore, the subject is still surrounded with a fair 
amount of uncertainty. 

MOLYBDENUM 
Molybdenum possesses the same characteristics as tungsten, 
but on account of its scarcity, is not used a great deal for com- 
mercial purposes. It is about twice as heavy and twice as 
effective as tungsten, and is supposed to harden at a little less 
temperature, but from tests made, nothing has been published 
showing its advantage over tungsten. 



ALLOYS AND THEIk EFFECT UPON STEEL 33 

SILICON 

Silicon prevents, to a large extent, defects such as air bubbles 
or blow holes forming pockets while steel is melting, as it mixes 
with the gases and oxide. When present in 1 per cent or more, 
it adds a great resiliency to steel, and in combination with either 
chrome, vanadium, or manganese, with a predominant carbon 
contents for element selected, it makes a splendid spring, and 
is used largely for its ability to absorb shocks. 

PHOSPHORUS 

Phosphorus is one of the impurities in steel, and it has been 
the object of steel makers for years to eliminate it. On cheap 
grades of steel, not subject to any abnormal strain or stress, 
0.1 per cent phosphorus is not objectionable, and will help 
machine ability by acting as a lubricant. High phosphorus 
has a tendency to make steel "cold short," i.e., low forging heats 
are apt to make checks or to start seams, and is also subject to 
cracking or opening up under sudden quenching. 

SULPHUR 

Sulphur is another impurity and high sulphur is even a greater 
detriment to steel than phosphorus. High sulphur up to 0.09 
per cent helps machining properties, but has a tendency to make 
the steel "hot short," i.e., subject to opening up cracks and seams 
at forging or rolling heats. Unless used in combination with 
manganese on commercial steel, sulphur should never exceed 
0.06 per cent and phosphorus over 0.08 per cent. 

Steel used for tool purposes should have as low phosphorus and 
sulphur contents as possible, not over 0.02 per cent, which can 
readily be made in both crucible and electric furnaces. 

We can sum up the various factors something as follows for 
ready reference. 

The ingredient Its effect 

Iron The basis of steel 

Carbon The determinative 

Sulphur A strength sapper 

Phosphorus The weak link 

Oxygen A strength destroyer 

Manganese For strength 

Nickel For strength and toughness 

Tungsten Hardener and heat resister 

Chromium For resisting shocks 

3 



34 



THE WORKING OF STEEL 



The ingredient Its effect 

Vanadium Purifier and fatigue resister 

Silicon Impurity and hardener 

Titanium ■ Removes nitrogen and oxygen 

Molybdenum Hardener and heat resister 

Aluminum Kills or deoxidizes steel 

PROPERTIES OF ALLOY STEELS 

The following table shows the percentages of carbon, manga- 
nese, nickel, chromium and vanadium in typical steel alloys for 
engineering purposes. It also gives the elastic limit, tensile 
strength, elongation and reduction of area of the various alloys, 
all being given the same heat treatment with a drawing tem- 
perature of 1,100°F. (600°C). The specimens were one inch 
rounds, machined after heat treatment. 

Tungsten is not shown in the table because it is seldom 
used in engineering construction steels and then usually in 
combination with chromium. Tungsten is used principally for 
the magnets of magnetos, to some extent in the manufacture of 
hacksaws, and for special tool steels. 





Table 1. — 


Properties of 


Alloy Steels 






a! 

O o 


Manganese, 
per cent 




2 a 
a ° 

C o 

o u 

3 a 


B 4» 

.3 s 

03 

g a 


- .5 

1 £ ' 

o S3 
"^3 a 


Tensile 
strength, 
lb. per sq. in. 


■H a 

j: 

J.s 

3 IN 


"o a 

^ 03 


0.27 


0.55 








49,000 


80,000 


30 


65 


0.27 


0.47 






0.26 


66,000 


98,000 


25 


52 


0.36 


0.42 








58,000 


90,000 


27 


'60 


,0 . 34 


0.87 






0.13 


82,500 


103,000 


22 


57 


0.45 


0.50 








65,000 


96,000 


22 


52 


0.43 


0.60 






0.32 


96,000 


122,000 


21 


52 


0.47 


0.90 






0.15 


102,000 


127,500 


23 


58 


0.30 


0.60 


3.40 






75,000 


105,000 


25 


67 


0.33 


0.63 


3.60 




0.25 


118,000 


142,000 


17 


57 


0.30 


0.49 


3.60 


L.70 




119,000 


149,500 


21 


60 


0.25 


0.47 


3.47 


1.60 


0.15 


139,000 


170,000 


18 


53 


0.25 


0.50 


2.00 


LOO 




102,000 


124,000 


25 


70 


[0.38 


0.30 


2.08 


1.16 




120,000 


134,000 


20 


57 


0.42 


0.22 


2.14 


L.27 


0.26 


145,000 


161,500 


16 


53 


0.36 


0.61 


1.46 ( 


).64 




117,600 


132,500 


16 


58 


0.36 


0.50 


1.30 ( 


).75 


0.16 


140,000 


157,500 


17 


54 


0.30 


0.50 


( 


).80 




90,000 


105,000 


20 


50 


0.23 


0.58 


( 


).82 


0.17 


106,000 


124,000 


21 


66 


0.26 


0.48 


( 


).92 


0.20 


112,000 


137,000 


20 


61 


0.35 


0.64 





L.03 


0.22 


132,500 


149,500 


16 


54 


0.50 


0.92 





.02 


0.20 


170,000 


186,000 


15 


45 



ALLOYS AND THEIR EFFECT UPON STEEL 



35 



NON-SHRINKING, OIL-HARDENING STEELS 
Certain steels have a very low rate of expansion and con- 
traction in hardening and are very desirable for test plugs, 
gages, punches and dies, for milling cutters, taps, reamers, hard 
steel bushings and similar work. 

It is recommended that for forging these steels it be heated 
slowly and uniformly to a bright red, but not in a direct flame 
or blast. Harden at a dull red heat, about 1,300°F. A clean coal 
or coke fire, or a good muffle-gas furnace will give best results. 
Fish oil is good for quenching although in some cases warm water 
will give excellent results. The steel should be kept moving in 
the bath until perfectly cold. Heated and cooled in this way 
the steel is very tough, takes a good cutting edge and has very 
little expansion or contraction which makes it desirable for long 
taps where the accuracy of lead is important. 
The composition of these steels is as follows: 

Per cent 

Manganese 1 . 40 to 1 . 60 

Carbon . 80 to . 90 

Vanadium 0.20 to 0.25 

£ g c S g Ft. Lb. Per Sq. In. 

Cliarpy Test 
BrineH So. 




Average \ie!d Point, Average Ultimate Strength, 
Lb. Per Sq. In. Thousands 

Fig. 11. — Effect of copper in steel. 



EFFECT OF A SMALL AMOUNT OF COPPER IN MEDIUM-CARBON 

STEEL 

This shows the result of tests by C. R. Hay ward and A. 
B. Johnston on two types of steel: one containing 0.30 per 



36 THE WORKING OF STEEL 

cent carbon, 0.012 per cent phosphorus, and 0.860 per cent 
copper, and the other 0.365 per cent carbon, 0.053 per cent 
phosphorus, and 0.030 per cent copper. The accompanying 
chart in Fig. 11 shows that high-copper steel has decided supe- 
riority in tensile strength, yield point and ultimate strength, 
while the ductility is practically the same. Hardness tests 
by both methods show high-copper steel to be harder than 
low-copper, and the Charpy shock tests show high-copper 
steel also superior to low-copper. The tests confirm those made 
by Stead, showing that the behavior of copper steel resembles 
that of nickel steel. The high-copper steels show finer grain 
than the low-copper. The quenched and drawn specimens of 
high-copper steel were found to be slightly more martensitic. 

HIGH-CHROMIUM OR RUST-PROOF STEEL 

High-chromium, or what is called stainless steel containing 
from 11 to 14 per cent chromium, was originally developed for 
cutlery purposes, but has in the past few years been used to a 
considerable extent for exhaust valves in airplane engines because 
of its resistance to scaling at high temperatures. 

Percentage 

Carbon 0.20 to 0.40 

Manganese, not to exceed . 50 

Phosphorus, not to exceed ■. 0. 035 

Sulphur, not to exceed 0. 035 

Chromium 11.50 to 14.00 

Silicon, not to exceed 0. 30 

The steel should be heated slowly and forged at a temperature 
above 1,750°F. preferably between 1,800 and 2,200°F. If forged 
at temperatures between 1,650 and 1,750°F. there is considerable 
danger of rupturing the steel because of its hardness at red heat. 
Owing to the air-hardening property of the steel, the drop- 
forgings should be trimmed while hot. Thin forgings should be 
reheated to redness before trimming, as otherwise they are liable 
to crack. 

The forgings will be hard if they are allowed to cool in air. 
This hardness varies over a range of from 250 to 500 Brinell, 
depending on the original forging temperature. 

Annealing can be done by heating to temperatures ranging 
from 1,290 to 1,380°F. and cooling in air or quenching in water or 
oil. After this treatment the forgings will have a hardness of 



ALLOYS AND THEIR EFFECT UPON STEEL 37 

about 200 Brinell and a tensile strength of 100,000 to 112,000 lb. 
per square inch. If softer forgings are desired they can be heated 
to a temperature of from 1,560 to 1,G50°F. and cooled very slowly. 
Although softer the forgings will not machine as smoothly as 
when annealed at the lower temperature. 

Hardening. — The forgings can be hardened by cooling in still 
air or quenching in oil or water from a temperature between 1,650 
and 1,750°F. 

The physical properties do not vary greatly when the carbon 
is within the range of composition given, or when the steel is 
hardened and tempered in air, oil, or water. 

When used for valves the following specification of physical 
properties have been used: 

Yield point, pounds per square inch 70,000 

Tensile strength, pounds per square inch 90,000 

Elongation in 2 in., per cent 18 

Reduction of area, per cent 50 

The usual heat treatment is to quench in oil from 1,650°F. 
and temper or draw at 1,100 to 1,200°F. One valve manufac- 
turer stated that valves of this steel are hardened by heating the 
previously annealed valves to 1,650°F. and cooling in still air. 
This treatment gives a scleroscope hardness of about 50. 

In addition to use in valves this steel should prove very satis- 
factory for shafting for water-pumps and other automobile parts 
subject to objectionable corrosion. 



Table 2. — Comparison op Physical Properties for High-chromium 
Steels of Different Carbon Content 



C 0.20 C 0.27 

Mn 0.45 Mn 0.50 
Cr 12.56 Cr 12.2-1 



C 0.50 
Cr 14.84 



Quenched in oil from degrees Fah- 
renheit 1,600 

Tempered at degrees Fahrenheit. . . 1,160 

Yield point, pounds per square inch . 78,300 
Tensile strength, pounds per square 

inch 104,600 

Elongation in 2 in., per cent 25.0 

Reduction of area, per cent 52.5 



1,600 


1,650 


1,080 


1,100 


75,000 


91,616 


104,250 


123,648 


23.5 


14.5 


51.4 


33.5 



38 



THE WORKING OF STEEL 



Table 3. — Comparison of Physical Properties between Air, Oil and 

Water-hardened Steel Having Chemical Analysis in 

Percentage op 



Carbon 0.24 

Manganese 0.30 

Phosphorus 0. 035 

Sulphur . 035 

Chromium 12.85 

Silicon 0.20 



Hardening 
medium 


Hardened 

from, 

degrees 

Fahrenheit 


Tempered 
at, degrees 
Fahrenheit 


Elastic 
limit, 
lb. per 
sq. in. 


Tensile 

strength, 

lb. per 

sq. in. 


Elonga- 
tion in 
2 in. 
per cent 


Reduc- 
tion of 
area, 
per cent 


Air 


1,650 


■ 


930 
1,100 
1,300 
1,380 
1,470 


158,815 
99,680 
70,785 
66,080 

70,785 


192,415 

120,065 

101,250 

98,335 

96,990 


13.0 
21.0 
26.0 
28.0 
27.0 


40.5 
59.2 
64.6 
63.6 
64.7 


Oil 


1,650 




930 

1,100 

1,300 

i 1,380 


163,070 

88,255 
77,950 
88,255 


202,720 
116,480 
105,505 

98,785 


8.0 
20.0 
25.5 

27.0 


18.2 
56.9 
63.8 
66.3 


Water. . . . 


1,650 




930 

1,100 

1,300 

. 1,380 


158,815 
90,270 
66,080 
67,200 


202,050 

120,735 

102,590 

97,890 


12.0 
22.0 
25.8 
27.0 


34.2 
59.8 
64.8 
65.2 



This steel can be drawn into wire, rolled into sheets and strips 
and drawn into seamless tubes. 

Corrosion. — This steel like any other steel when distorted by 
cold working is more sensitive to corrosion and will rust. Rough 
cut surfaces will rust. Surfaces finished with a fine cut are less 
liable to rust. Ground and polished surfaces are . practically 
immune to rust. 

When chromium content is increased to 16 to 18 per cent and 
silcon is added, from 2 to 4 per cent, thus steel becomes rust 
proof in its raw state, as soon as the outside surface is removed. 
It does not need to be heat-treated in any way. These composi- 
tions are both patented. 



ALLOYS AND THEIR EFFECT UPON STEEL 



39 



S. A. E. STANDARD STEELS 

The following steel specifications are considered standard by 
the Society of Automotive Engineers and represents automobile 
practice in this country. These tables give the S. A. E. number, 
the composition of the steel and the heat treatment. These are 
referred to by letter — , the heat treatments being given in detail 
on pages 134 to 137 in Chapter 8. It should be noted that 
the percentage of the different ingredients desired, is the mean, or 
halfway between the minimum and maximum. 







Table 4.— 


-Carbon Steels 




S. A. E. 

Specification 

no. 


Carbon Manganese 








(minimum 
and 


(minimum 
and 


Phosphorus 
(maximum) 


Sulphur 
(maximum) 


Heat 
treatment 


maximum) 


maximum) 








1,010 


0.05 to 0. 15 


0.30 to 0.60 


0.045 


0.05 


Quench at 1,500 


1,020 


0.15 to 0.25 


. 30 to . 60 


0.045 


0.05 


A or B 


1,025 


0.20 to 0.30 


0.50 to 0.80 


0.045 


0.05 


H 


1,035 


. 30 to . 40 


0.50 to 0.80 


0.045 


0.05 


H, D or E 


1,045 


0.40 to 0.50 


0.50 to 0.80 


0.045 


0.05 


H, D or E 


1,095 


. 90 to 1 . 05 


0.25 to 0.50 


0.040 


0.05 


F 





Table 5. — Screw Stock 




S. A. E. 
Specification no. 


Carbon 


Manganese 


Phosphorus 
(maximum) 


Sulphur 


1,114 


0.08 to 0.20 


0.30 to 0.80 


0.12 


0.06 to0.12 







Table 6. 


— NlCKEI 


j Steels 






S. A. E. 
Specifica- 
tion no. 


Carbon 


Manganese 


Phos- 


Sul- 


Nickel 




(minimum 
and 

maximum) 


(minimum 

and 
maximum) 


phorus 
(maxi- 
mum) 


phur 

(maxi- 
mum) 


(minimum 

and 
maximum) 


Heat 
treatment 


2,315 


0.10 to 0.20 


0.50 to 0.80 


0.04 


0.045 


3.25 to 3.75 


G, H or K 


2,320 


0.15 to 0.25 


0.50 to 0.80 


0.04 


0.045 


3.25 to 3.75 


G, H or K 


2,330 


0.25 to 0.35 


0.50 to 0.80 


0.04 


0.045 


3 . 25 to 3 . 75 


H or K 


2,335 


0.30 to 0.40 


0.50 to 0.80 


0.04 


0.045 


3 . 25 to 3 . 75 


H or K 


2,340 


0.35 to 0.45 


0.50 to 0.80 


0.04 


0.045 


3 . 25 to 3 . 75 


H or K 


2,345 


0.40 to 0.50 


0.50 to 0.80 


0.04 


0.045 


3.25 to 3.75 


H or K 



40 



THE WORKING OF STEEL 



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ALLOYS AND THEIR EFFECT UPON STEEL 



41 



Table 8. — Chromium Steels 



S. A. E. 
Specifica- 
tion no. 


Carbon 


Manganese 


Phos- 


Sul- 


Chromium 




(minimum 

and 
maximum) 


(minimum 
and 

maximum) 


phorus 
(maxi- 
mum) 


phur 
(maxi- 
mum) 


(minimum 

and 
maximum) 


Heat 
treatment 


5,120 


0.15 to 0.25 


* 


0.04 


0.045 


0.65 to 0.85 


B 


5,140 


0.35 to 0.45 


* 


0.04 


0.045 


. 65 to . 85 


H or D 


5,165 


. 60 to . 70 


* 


0.04 


0.045 


. 65 to . S5 


H or D 


5,195 


. 90 to 1 . 05 


0.20 to 0.45 


0.03 


0.03 


0.90 to 1.10 


M, P or R 


51,120 


1 . 10 to 1 . 30 


0.20 to 0.45 


0.03 


0.03 


. 90 to 1 . 10 


M, P or R 


5,295 


. 90 to 1 . 05 


. 20 to . 45 


0.03 


0.03 


1.10 to 1.30 


M, P or R 


52,120 


1 . 10 to 1 . 30 


0.20 to 0.45 


0.03 


0.03 


1 . 10 to 1 . 30 


M, P or R 



- Two types of steel are available in this class, one with manganese 0.25 to 0.50 per cent 
(0.35 per cent desired), and silicon not over 0.20 per cent; the other with manganese 0.60 
to 0.S0 per cent (0.70 per cent desired), and silicon 0.15 to 0.50 per cent. 



Table 9. — Chromium-vanadium Steels 



S. A. E. 


Carbon 


Manganese 


Phos- 


Sul- 


1 
Chromium 


Vana- 




Specifica- 


(minimum 


(minimum 


phorus 


phur 


(minimum 


dium 


treat- 




and 


and 


(maxi- 


(maxi- 


and 


(mini- 




tion no. 














ment 




maximum) 


maximum) 


mum) 


mum) 


maximum) 


mum) 




6,120 


0.15 to0.25 


0.50 to 0.80 


0.04 


0.04 


0.80 to 1.10 


0.15 


S 


6,125 


0.20 to 0.30 


0.50 to 0.80 


0.04 


0.04 


0.80 to 1.10 


0.15 


S or T 


6,130 


0.25 to 0.35 


0.50 to 0.80 


0.04 


0.04 


0.80 to 1.10 


0.15 


T or U 


6435 


0.30 to 0.40 


. 50 to . 80 


0.04 


0.04 


0.80 to 1.10 


0.15 


T or U 


6,140 


0.35 to 0.45 


0.50 to 0.80 


0.04 


0.04 


. 80 to 1 . 10 


0.15 


T or U 


6,145 


0.40 to 0.50 


0.50 to 0.80 


0.04 


0.04 


0.80 to 1.10 


0.15 


U 


6,150 


. 45 to . 55 


0.50 to 0.80 


0.04 


0.04 


0.80 to 1.10 


0.15 


U 


6,195 


0.90 to 1.05 


0.20 to 0.45 


0.03 


0.03 


0.80 to 1.10 


0.15 


u 





Table 


10.— SlLICO- 


MANGANESE STEELS 




S. A. E. 
Specifica- 
tion no. 


Carbon 

(minimum 

and 
maximum) 


Manganese 
(minimum 

and 
maximum) 


Phos- 
phorus 
(maxi- 
mum) 


Sul- 
phur 
(maxi- 
mum) 


Silicon 
(minimum 

and 
maximum) 


Heat 

treat- 
ment 


9,250 
9,260 


0.45 to 0.55 
0.55 to 0.'65 


0.60 to 0.80 0.045* 
0.50 to 0.70 ! 0.045* 


0.045 
0.045 


1.80 to 2.10 
1 . 50 to 1 . 80 


V 
V 



* Steel made by the acid process may contain maximum 0.05 phosphorus. 



42 THE WORKING OF STEEL 

LIBERTY MOTOR CONNECTING RODS 

The requirements for materials for the Liberty motor connect- 
ing rods are so severe that the methods of securing the desired 
qualities will be of value in other lines. The original specifica- 
tions called for chrome-nickel but the losses due to the difficulty 
of handling caused the Lincoln Motor Company to suggest the 
substitution of chrome-vanadium steel, and thus was accepted 
by the Signal Corps. The rods were accordingly made from 
chronium-vanadium steel, containing carbon, 0.30 to 0.40 per 
cent; manganese, 0.50 to 0.80 per cent; phosphorus, not over 0.04 
per cent; sulphur, not over 0.04 per cent; chromium, 0.80 to 
1.10 per cent; vanadium, not less than 0.15 per cent. This steel 
is ordinarily known in the trade as 0.35 carbon steel, S. A. E., 
specification 6,135, which provides a first rate quality steel for 
structural parts that are to be heat-treated. The fatigue resist- 
ing or endurance qualities of this material are excellent. It has 
a tensile strength of 150,000 lb. minimum per square inch; 
elastic limit, 115,000 lb. minimum per square inch; elongation, 
45 per cent minimum in 2 in.; and minimum reduction in area, 
45 per cent. 

The original production system as outlined for the manu- 
facturers had called for a heat treatment in the rough-forged 
state for the connecting rods, and then semi-machining the rod 
forgings before giving them the final treatment. The Lincoln 
Motor Company insisted from the first that the proper method 
would be a complete heat treatment of the forging in the rough 
state, and machining the rod after the heat treatment. After a 
number of trial lots, the Signal Corps acceded to the request 
and production was immediately increased and quality benefited 
by the change. This method was later included in a revised 
specification issued to all producers. 

The original system was one that required a great deal of 
labor per unit output. The Lincoln organization developed a 
method of handling connecting rods whereby five workmen ac- 
complished the same result that would have required about 30 
or 32 by the original method. Even after revising the specifica- 
tion so as to allow complete heat treatments in the rough-forged 
state, the ordinary methods employed in heat-treating would 
have required 12 to 15 men. With the fixtures employed, 
five men could handle 1,300 connecting rods, half of which are 
plain and half, forked, in a working period of little over 7 hr. 



ALLOYS AND THEIR EFFECT UPON STEEL 43 















t'^ 


i;- 




"fm. 




- • -" mmtHf"- " 


s;»'^ MIII |!*'S 










fljBL. A ^fmlm 


lifli 


: .. ] 



Fig. 12. — Rack for holding rods. 




Fig. 13. — Sliding rods into tank. 



44 THE WORKING OF STEEL 

The increase in production was gained by devising fixtures 
which enabled fewer men to handle a greater quantity of parts 
with less effort and in less time. 

In heat-treating the forgings were laid on a rack or loop A, 
Fig. 12, made of 1^-in. double extra-heavy pipe, bent up with 
parallel sides about 9 in. apart, one end being bent straight across 
and the other end being bent upward so as to afford an easy 
grasp for the hook. Fifteen rods were laid on each loop, there 
being four loops of rods charged into a furnace with a hearth 
area of 36 by 66 in. The rods were charged at a temperature of 
approximately 900°F. They were heated for refining over a 
period of 3 hr. to 1,625°F., soaked 15 min, at this degree of 
heat and quenched in soluble quenching oil. 

In pulling the heat to quench the rods, the furnace door was 
raised and the operator pulls one of the loops A, Fig. 13 forward 
to the shelf of the furnace, supporting the straight end of the 
loop by means of the porter bar B. They swung the loop of rods 
around from the furnace shelf and set the straight end of the 
loop on the edgr of the quenching tank, then raise the curved 
end C, by means of their hook D so that all the rods on the loop 
slide into the oil bath. 

Before the rods cooled entirely, the baskets in the quenching 
tank were raised and the oil allowed to partly drain off the forg- 
ings, and they were stacked on curved-end loops or racks and 
charged into the furnace for the second or hardening heat. The 
temperature of the furnace was raised in 1}^ hr. to 1,550°F., the 
rods soaked for 15 min. at this degree of heat and quenched in 
the same manner as above. 

They were again drained while yet warm, placed on loops and 
charged into the furnace for the third or tempering heat. The 
temperature of the furnace was brought to 1,100°F. in 1 hr., 
and the rods soaked at this degree of heat for 1 hr. They were 
then removed from the furnace the same as for quenching, but 
were dumped onto steel platforms instead of into the quenching 
oil, and allowed to cool on these steel platforms down to the room 
temperature. 

PICKLING THE FORGINGS 

The forgings were then pickled in a hot solution of either niter 
cake or sulphuric acid and water at a temperature of 170°F., 
and using a solution of about 25 per cent. The solution was 



ALLOYS AND THEIR EFFECT UPON STEEL 45 

maintained at a constant point by taking hydrometer readings 
two or three times a day maintaining a reading of about 1,175. 
Sixty forked or one hundred single rods were placed in wooden 
racks and immersed in a lead-lined vat 30 by 30 by 5 ft. long. 
The rack was lowered or lifted by means of an air hoist and the 
rods were allowed to stay in solution from y% to 1 hr. depending 
on the amount of scale. The rods were then swung and lowered 
in the rack into running vat of running hot water until all trace 
of the acid was removed. 

The rod was finally subjected to Brinell test. This shows 
whether or not the rod has been heat-treated to the proper 
hardness. If the rods did not read between 241 and 277, they 
were re-treated until the proper hardness is obtained. 



CHAPTER IV 

APPLICATION OF LIBERTY ENGINE MATERIALS TO THE 
AUTOMOTIVE INDUSTRY 1 

The success of the Liberty engine program was an engineering- 
achievement in which the science of metallurgy played an 
important part. The reasons for the use of certain materials 
and certain treatments for each part are given with recommen- 
dations for their application to the problems of automotive 
industry. 

The most important items to be taken into consideration in 
the selection of material for parts of this type are uniformity 
and machineability. It has been demonstrated many times 
that the ordinary grades of bessemer screw stock are unsatis- 
factory for aviation purposes, due to the presence of excessive 
amounts of unevenly distributed phosphorus and sulphide 
segregations. For this reason, material finished by the basic 
open hearth process was selected, in accordance with the following 
specifications: Carbon, 0.150 to 0.250 per cent; manganese, 
0.500 to 0.800 per cent; phosphorus, 0.045 maximum per cent; 
sulphur, 0.060 to 0.090 per cent. 

This material in the cold-drawn condition will show: Elastic 
limit, 50,000; lb. per square inch, elongation in 2 in., 10 per cent 
reduction of area, 35 per cent. 

This material gave as uniform physical properties as S. A. E. 
No. 1020 steel and at the same time was sufficiently free cutting 
to produce a smooth thread and enable the screw-machine 
manufacturers to produce, to the same thread limits, approxi- 
mately 75 per cent as many parts as from bessemer screw stock. 

There are but seven carbon-steel carbonized parts on the 
Liberty engine. The most important are the camshaft, the 
camshaft rocker lever roller and the tappet. The material used 
for parts of this type was S. A. E. No. 1,020 steel, which is of 
the following chemical analysis: Carbon 0.150 to 0.250 per cent; 
manganese, 0.300 to 0.600 per cent; phosphorus, 0.045 maximum 
per cent; sulphur, 0.050 maximum per cent. 

1 Paper presented at the summer meeting of the S. A. E. at Ottawa Beach 
in June, 1919. 

46 



APPLICATION OF LIBERTY ENGINE MATERIALS 47 

The heat treatment consisted in carbonizing at a temperature 
of from 1,650 to 1,700°F. for a sufficient length of time to secure 
the proper depth of case and cool slowly or quench; then reheat 
to a temperature of 1,380 to 1,430°F. to refine the grain of the 
case, and quench in water. The only thing that should limit 
the rate of cooling from the carbonizing heat is distortion. 
Camshaft rocker lever rollers and tappets, as well as gear pins, 
were quenched directly from the carbonizing heat in water and 
then case-refined and rehardened by quenching in water from 
a temperature of from 1,380 to 1,430°F. 

The advantage of direct quenching lies in the production of 
fiber. The rapid cooling causes the strength of the amorphous 
intercrystalline material to be greater than that of the crystals 
themselves, which produces the same practical results as are 
obtained by increasing the amount of amorphous intercrystalline 
material by refining the grain of the core by a 1,625 to 1,650°F. 
quench in oil. The existence of this condition causes the 
shock-resisting properties of the part to be increased greatly. 

Another advantage obtained from rapid cooling from the 
carbonizing heat is the retaining of the majority of the excess 
cementite in solution which produces a less brittle case and by so 
doing reduces the liability of grinding checks and chipping of 
the case in actual service. 

In the case of the camshaft, it is not possible to quench directly 
from the carbonizing heat because of distortion and therefore 
excessive breakage during straightening operations. All Liberty 
camshafts were cooled slowly from carbonizing heat and hardened 
by a single reheating to a temperature of from 1,380 to 1,430°F. 
and quenching in water. 

Considerable trouble has always been experienced in obtaining 
uniform hardness on finished camshafts. This is caused by 
insufficient water circulation in the quenching tank, which allows 
the formation of steam pockets to take place, or by decarbon- 
ization of the case during heating by the use of an overoxidizing 
flame. Another cause, which is very often overlooked, is due 
to the case being ground off one side of cam more than the other 
and is caused by the roughing master cam.' being slightly different 
from the finishing master cam. Great care should be taken to 
see that this condition does not occur, especially when the 
depth of case is between }^2 and %4 in. 



48 THE WORKING OF STEEL 

CARBON-STEEL FORGINGS 

Low-stressed carbon-steel forgings include such parts as 
carbureter control levels, etc. The important criterion for 
parts of this type is ease of fabrication and freedom from over- 
heated and burned forgings. The material used for such parts 
was S. A. E. No. 1,030 steel, which is of the following chemical 
composition: Carbon, 0.250 to 0.350 percent; manganese, 0.500 
to 0.800 per cent; phosphorus, 0.045 maximum per cent; sulphur, 
0.050 maximum per cent. 

To obtain good machineability, all forgings produced from 
this steel were heated to a temperature of from 1,575 to 1,625°F. 
to refine the grain of the steel thoroughly and quenched in water 
and then tempered to obtain proper machineability by heating 
to a temperature of from 1,000 to 1,100°F. and cooled slowly or 
quenched. 

Forgings subjected to this heat treatment are free from hard 
spots and will show a Brinell hardness of 177 to 217, which is 
proper for all ordinary machining operations. Great care 
should be taken not to use steel for parts of this type containing 
less than 0.25 per cent carbon, because the lower the carbon the 
greater the liability of hard spots, and the more difficult it 
becomes to eliminate them. The only satisfactory method so 
far in commercial use for the elimination of hard spots is to give 
forgings a very severe quench from a high temperature followed 
by a proper tempering heat to secure good machineability as 
outlined above. 

The important carbon-steel forgings consisted of the cylinders, 
the propeller-hubs, the propeller-hub flange, etc. The material 
used for parts of this type was S. A. E. No. 1,045 steel, which is 
of the following chemical composition : Carbon, 0.400 to 0.500 per 
cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 
maximum per cent; sulphur, 0.050 maximum per cent. 

All forgings made from this material must show, after heat 
treatment, the following minimum physical properties: Elastic 
limit, 70,000; lb. per square inch, elongation in 2 in., 18 per 
cent, reduction of area, 45; per cent, Brinell hardness, 217 to 
255. 

To obtain these physical properties, the forgings were quenched 
in water from a temperature of 1,500 to 1,550°F., followed 
by tempering to meet proper Brinell requirements by heating 
to a temperature of 1,150 to 1,200°F. and cooled slowly or 



APPLICATION OF LIBERTY ENGINE MATERIALS 49 

quenched. No trouble of any kind was ever experienced with 
parts of this type. 

The principal carbon-steel pressed parts used on the Liberty 
engine were the water jackets and the exhaust manifolds. The 
material used for parts of this type was S. A. E. No. 1,010 steel, 
which is of the following chemical composition: Carbon, 0.050 
to 0.150 per cent; manganese, 0.300 to 0.600 per cent; phosphorus, 
0.045 maximum per cent; sulphur, 0.045 maximum per cent. 

No trouble was experienced in the production of any parts 
from this material with the exception of the water jacket. Due 
to the particular design of the Liberty cylinder assembly, many 
failures occurred in the early days, due to the top of the jacket 
cracking from fatigue. It was found that these fatigue failures 
were caused primarily from the use of jackets which showed 
small scratches or die marks at this joint and secondarily bj' 
improper annealing of the jackets themselves between the 
different forming operations. By a careful inspection for die 
marks and by giving the jackets 1,400°F. annealing before the 
last forming operation, it was possible to completely eliminate 
the trouble encountered. 

HIGHLY STRESSED PARTS 

The highly stressed parts on the Libert}' engine consisted of 
the connecting-rod bolt, the main-bearing bolt, the propeller- 
hub key, etc. The material used for parts of this type was 
selected at the option of the manufacturer from standard S. A. E. 
steels, the composition of which are given in Table 11. 

Table 11.— Composition of S. A. E. Steels Nos. 2,330, 3,135 and 6,130 

Steel No 2,330 3,135 6,130 

Carbon, minimum 0.250 0.300 0.250 

Carbon, maximum . 350 . 400 . 450 

Manganese, minimum 0.500 0.500 0.500 

Manganese, maximum . 800 . 800 . 800 

Phosphorus, maximum 0.045 0.040 0.040 

Sulphur, maximum . 045 . 045 0. 045 

Nickel, minimum 3 . 250 1 . 000 

Nickel, maximum 3 . 750 1 . 500 

Chromium, minimum . 450 . 800 

Chromium, maximum . 750 1 . 100 

Vanadium, minimum 0. 150 

4 



50 THE WORKING OF STEEL 

All highly stressed parts on the Liberty engine must show, 
after heat treatment, the following minimum physical properties : 
Elastic limit, 100,000; lbs. per square inch, elongation in 2 in., 
16 per cent; reduction of area, 45 per cent; scleroscope hardness, 
40 to 50. 

The heat treatment employed to obtain these physical proper- 
ties consisted in quenching from a temperature of 1,525 to 
1,575°F., in oil, followed by tempering at a temperature of 
from 925 to 975°F. 

Due to the extremely fine limits used on all threaded parts 
for the Liberty engine, a large percentage of rejection was due 
to warpage and scaling of parts. To eliminate this objection, 
many of the Liberty engine builders adopted the use of heat- 
treated and cold-drawn alloy steel for their highly stressed 
parts. On all sizes up to and including % in. in diameter, the 
physical properties were secured by merely normalizing the 
hot-rolled bars by heating to a temperature of from 1,525 to 
1,575°F., and cooling in air, followed by the usual cold-drawing 
reductions. For parts requiring stock over % in. in diameter, 
the physical properties desired were obtained by quenching and 
tempering the hot-rolled bars before cold-drawing. It is the 
opinion that the use of heat-treated and. cold-drawn bars is very 
good practice, provided proper inspection is made to guarantee 
the uniformity of heat treatment and, therefore, the uniformity 
of the physical properties of the finished parts. 

The question has been asked many times by different manu- 
facturers, as to which alloy steel offers the best machineability 
when heat-treated to a given Brinell hardness. The general 
consensus of opinion among the screw-machine manufacturers 
is that S. A. E. No. 6,130 steel gives the best machineability and 
that S. A. E. No. 2,330 steel would receive second choice of the 
three specified. 

In the finishing of highly stressed parts for aviation engines, 
extreme care must be taken to see that all tool marks are elimi- 
nated, unless they are parallel to the axis of strain, and that 
proper radii are maintained at all changes of section. This is 
of the utmost importance to give proper fatigue resistance to the 
part in question. 

GEARS 

The material used^for all gears on the Liberty engine was 
selected at the option of the manufacturer from the following 



APPLICATION OF LIBERTY ENGINE MATERIALS 51 

standard S. A. E. steels, the composition of which are given 
in Table 12. 

Table 12.- — Composition of Steels Nos. X-3,340 and 6,140 

Steel No X-3,340 6,140 

Carbon, minimum 0.350 0.350 

Carbon, maximum 0.450 0.450 

Manganese, minimum 0.450 0.500 

Manganese, maximum . 750 . 800 

Phosphorus, maximum . 040 . 040 

Sulphur, maximum 0.045 0.045 

Nickel, minimum 2 . 750 

Nickel, maximum 3 . 250 

Phosphorus, maximum . 700 . 800 

Phosphorus, maximum . 950 1 . 100 

Vanadium, minimum 0. 150 

All gears were heat-treated to a scleroscope hardness of from 
55 to 65. The heat treatment used to secure this hardness 
consisted in quenching the forgings from a temperature of 1,550 
to 1,600°F. in oil and annealing for good machineability at a 
temperature of from 1,300 to 1,350°F. Forgings treated in 
this manner showed a Brinell hardness of from 177 to 217. 

RATE OF COOLING 

At the option of the manufacturer, the above treatment of 
gear forgings could be substituted by normalizing the forgings at 
a temperature of from 1,550 to 1,600°F. The most important 
criterion for proper normalizing consisted in allowing the forgings 
to cool through the critical temperature of the steel, at a rate 
not to exceed 50°F. per hour. For the two standard steels used, 
this consisted in cooling from the normalizing temperature 
down to a temperature of 1,100°F., at the rate indicated. Forg- 
ings normalized in this manner will show a Brinell hardness of 
from 177 to 217. The question has been repeatedly asked as to 
which treatment will produce the higher quality finished part. 
In answer to this i will state that on simple forgings of com- 
paratively small section, the normalizing treatment will produce 
a finished part which is of equal quality to that of the quenched 
and annealed forgings. However, in the case of complex forg- 
ings, or those of large section, more uniform physical properties 
of the finished part will be obtained by quenching and annealing 
the forgings in the place of normalizing. 



52 THE WORKING OF STEEL 

The heat treatment of the finished gears consisted of quenching 
in oil from a temperature of from 1,420 to 1,440°F. for the No. 
X-3,340 steel, or from a temperature of from 1,500 to 1,540°F. 
for No. 6,140 steel, followed by tempering in saltpeter or in an 
electric furnace at a temperature of from 650 to 700°F. 

The question has been asked by many engineers, why is the 
comparatively low scleroscope hardness specified for gears? 
The reason for this is that at best the life of an aviation engine 
is short, as compared with that of an automobile, truck or 
tractor, and that shock resistance is of vital importance. A 
sclerescope hardness of from 55 to 65 will give sufficient resistance 
to wear to prevent replacements during the life of an aviation 
engine, while at the same time this hardness produces approxi- 
mately 50 per cent greater shock-resisting properties to the gear. 
In the case of the automobile, truck or tractor, resistance to 
wear is the main criterion and for that reason the higher hardness 
is specified. 

Great care should be taken in the design of an aviation engine 
gear to eliminate sharp corners at the bottom of teeth as well as in 
keyways. Any change of section in any stressed part of an 
aviation engine must have a radius of at least 3^2 in- to give proper 
shock and fatigue resistance. This fact has been demonstrated 
many times during the Liberty engine program. 

CONNECTING RODS 

The material used for all connecting rods on the Liberty 
engine was selected at the option of the manufacturer from one of 
two standard S. A. E. steels, the composition of which are given 
in Table 13. 

Table 13. — Composition of Steels Nos. X-3,335 and 6,135 

Steel No X-3,335 6,135 

Carbon, minimum 0.300 0.300 

Carbon, maximum 0.400 0.400 

Manganese, minimum 0.450 0.500 

Manganese, maximum . 750 . 800 

Phosphorus, maximum 0.040 0.040 

Sulphur, maximum . 045 . 045 

Nickel, minimum 2 . 750 

Nickel, maximum 3 . 250 

Chromium, minimum 0. 700 0. 800 

Chromium, maximum 0. 950 1 . 100 

Vanadium, minimum. 0. 150 



APPLICATION OF LIBERTY ENGINE MATERIALS 53 

All connecting rods were heat-treated to show the following 
minimum physical properties; Elastic limit, 105,000 lb. per 
square inch: elongation in 2 in., 17.5; per cent, reduction of area 
50.0; per cent., Brinell hardness, 241 to 277. 

The heat treatment used to secure these physical properties 
consisted in normalizing the forgings at a temperature of from 
1,550 to 1,600°F., followed by cooling in the furnace or in air. 
The forgings were then quenched in oil from a temperature of 
from 1,420 to 1,440°F. for the No. X-3,335 steel, or from a tem- 
perature of from 1,500 to 1,525°F. for No. 6,135 steel, followed 
by tempering at a temperature of from 1,075 to 1,150°F. At 
the option of the manufacturer, the normalizing treatment could 
be substituted by quenching the forgings from a temperature of 
from 1,550 to 1,600°F., in oil, and annealing for the best machine- 
ability at a temperature of from 1,300 to 1,350°F. The double 
quench, however, did not prove satisfactory on No. X-3,335 
steel, due to the fact that it was necessary to remove forgings 
from the quenching bath while still at a temperature of from 300 
to 500 °F. to eliminate any possibility of cracking. In view of 
the fact that this practice is difficult to carry out in the average 
heat-treating plant, considerable trouble was experienced. 

The most important criterion in the production of aviation 
engine connecting rods is the elimination of burned or severely 
overheated forgings. Due to the particular design of the forked 
rod, considerable trouble was experienced in this respect because 
of the necessitjr of reheating the forgings before they are com- 
pletely forged. As a means of elimination of burned forgings, 
test lugs were forged on the channel section as well as on the top 
end of fork. After the finish heat treatment, these test lugs were 
nicked and broken and the fracture of the steel carefully ex- 
amined. This precaution made it possible to eliminate burned 
forgings as the test lugs were placed on sections which would be 
most likely to become burned. 

There is a great difference of opinion among engineers as to 
what physical properties an aviation engine connecting rod should 
have. Many of the most prominent engineers contend that a 
connecting rod should be as stiff as possible. To produce rods 
in this manner in any quantity, it is necessary for the final heat 
treatment to be made on the semi-machined rod. This practice 
would make it necessary for a larger percentage of the semi- 
machined rods to be cold-straightened after the finish heat 



54 THE WORKING OF STEEL 

treatment. The cold-straightening operation on a part having 
important functions to perform as a connecting rod is extremely 
dangerous. 

In view of the fact that a connecting rod functions as a strut, 
it is considered that this part should be only stiff enough to 
prevent any whipping action during the running of the engine. 
The greater the fatigue-resisting property that one can put into 
the rod after this stiffness is reached, the longer the life of the 
rod will be. This is the reason for the Brinell limits mentioned 
being specified. 

In connection with the connecting rod, emphasis must be 
laid on the importance of proper radii at all changes of section. 
The connecting rods for the first few Liberty engines were 
machined with sharp corners at the point where the connecting- 
rod bolt-head fits on assembly. On the first long endurance 
test of a Liberty engine equipped with rods of this type, failure 
resulted from fatigue starting at this point. It is interesting to 
note that every rod on the engine which did not completely fail 
at this point had started to crack. The adoption of a ;H$2-in. 
radius at this point completely eliminated fatigue failures on 
Liberty rods. 

CRANKSHAFT 

The crankshaft was the most highly stressed part of the 
entire Liberty engine, and, therefore, every metallurgical pre- 
caution was taken to guarantee the quality of this part. The 
material used for the greater portion of the Liberty crankshafts 
produced was nickel-chromium steel of the following chemical 
composition: Carbon, 0.350 to 0.450 per cent; manganese, 0.300 
to 0.600 per cent; phosphorus, 0.040 maximum per cent; sulphur, 
0.045 maximum per cent; nickel, 1.750 to 2.250 per cent; 
chromium, 0.700 to 0.900 per cent. 

Each crankshaft was heat-treated to show the following 
minimum physical properties: Elastic limit, 116,000 lb. per 
square inch; elongation in 2 in., 16 per cent, reduction of area, 
50 per cent, Izod impact, 34 ft. -lb.; Brinell hardness, 266 to 321. 

For every increase of 4,000 lb. per square inch in the elastic 
limit above 116,000 lb. per square inch, the minimum Izod impact 
required was reduced 1 ft.-lb. 

The heat treatment used to produce these physical properties 
consisted in normalizing the forgings at a temperature of from 
1,550 to 1,600°F., followed by quenching in water at a temper- 



APPLICATION OF LIBERTY ENGINE MATERIALS 55 

ature of from 1,475 to 1,525°F. and tempering at a temperature 
of from 1,000 to 1,100°F. It is absolutely necessary that the 
crankshafts be removed from the quenching tank before being- 
allowed to cool below a temperature of 500°F., and immediately 
placed in the tempering furnace to eliminate the possibility of 
quenching cracks. 

A prolongation of not less than the diameter of the forging 
bearing was forged on one end of each crankshaft. This was 
removed from the shaft after the finish heat treatment, and 
physical tests were made on test specimens which were cut 
from it at a point half way between the center and the surface. 
One tensile test and one impact test were made on each crank- 
shaft, and the results obtained were recorded against the serial 
number of the shaft in question. This serial number was carried 
through all machining operations and stamped on the cheek of 
the finished shaft. In addition to the above tensile and impact 
tests, at least two Brinell hardness determinations were made 
on each shaft. 

All straightening operations on the Liberty crankshaft which 
were performed below a temperature of 500°F. were followed by 
retempering at a temperature of approximately 200°F. below 
the original tempering temperature. 

Another illustration of the importance of proper radii at all 
changes of section is given in the case of the Liberty crankshaft. 
The presence of tool marks or under cuts must be completely 
eliminated from an aviation engine crankshaft to secure proper 
service. During the duration of the Liberty program, four 
crankshafts failed from fatigue, failures starting from sharp 
corners at bottom of propeller-hub keyway. Two of the shafts 
that failed showed torsional spirals running more than completely 
around the shaft. As soon as this difficulty was removed no 
further trouble was experienced. 

One of the most important difficulties encountered in connec- 
tion with the production of Liberty crankshafts was hair-line 
seams. The question of hair-line seams has been discussed to 
greater length by engineers and metallurgists during the war than 
any other single question. Hair-line seams are caused by small 
non-metallic inclusions in the steel. There is every reason to 
believe that these inclusions are in the greater majority of cases 
manganese sulphide. There is a great difference of opinion as to 
the exact effect of hair-line seams on the service of an aviation 



56 THE WORKING OF STEEL 

engine crankshaft. It is the opinion of many that hair-line seams 
do not in any way affect the endurance of a crankshaft in service, 
provided they are parallel to the grain of the steel and do not 
occur on a fillet. Of the 20,000 Liberty engines produced, fully 
50 per cent of the crankshafts used contain hair-line seams but 
not at the locations mentioned. There has never been a failure 
of a Liberty crankshaft which could in any way be traced to 
hair-line seams. 

It was found that hair-line seams occur generally on high 
nickel-chromium steels. One of the main reasons why the com- 
paratively mild analysis nickel-chromium steel was used was due 
to the very few hair-line seams present in it. It was also deter- 
mined that the hair lines will in general be found near the surface 
of the forgings. For that reason, as much finish as possible was 
allowed for machining. A number of tests have been made on 
forging bars to determine the depths at which hair-line seams are 
found, and many cases came up in which hair-line seams were 
found % in. from the surface of the bar. This means that in case 
a crankshaft does not show hair-line seams on the ground surface 
this is no indication that it is free from such a defect. 

One important peculiarity of nickel-chromium steel was 
brought out from the results obtained on impact tests. This 
peculiarity is known as "blue brittleness. " Just what the effect 
of this is on the service of a finished part depends entirely upon 
the design of the particular part in question. There have been 
no failures of any nickel-chromium steel parts in the automotive 
industry which could in any way be traced to this phenomena. 

Whether or not nickel-chromium-steel forgings will show "blue 
brittleness" depends entirely upon the temperature at which they 
are tempered and their rate of cooling from this temperature. 
The danger range for tempering nickel-chromium steels is be- 
tween a temperature of from 400 to 1,100°F. From the data so 
far gathered on this phenomena, it is necessary that the nickel- 
chromium steel to show "blue brittleness" be made by the acid 
process. There has never come to my attention a single instance 
in which basic open hearth steel has shown this phenomena. 
Just why the acid open hearth steel should be sensitive to "blue 
brittleness" is not known. 

All that is necessary to eliminate the presence of "blue brittle- 
ness" is to quench all nickel-chromium-steel forgings in water 
from their tempering temperature. The last 20,000 Liberty 
crankshafts that were made were quenched in this manner. 



APPLICATION OF LIBERTY ENGINE MATERIALS 57 

PISTON PIN 

The piston pin on an aviation engine must possess maximum 
resistance to wear and to fatigue. For this reason, the piston 
pin is considered, from a metallurgical standpoint, the most 
important part on the engine to produce in quantities and still 
possess the above characteristics. The material used for the 
Liberty engine piston pin was S. A. E. No. 2315 steel, which is of 
the following chemical composition: Carbon, 0.100 to 0.200 per 
cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.040 
maximum per cent; sulphur, 0.045 maximum per cent; nickel, 
3.250 to 3.750 per cent. 

Each finished piston pin, after heat treatment, must show a 
minimum scleroscope hardness of the case of 70, a scleroscope 
hardness of the core of from 35 to 55 and a minimum crushing 
strength when supported as a beam and the load applied at the 
center of 35,000 lb. The heat treatment used to obtain the above 
physical properties consisted in carburizing at a temperature not 
to exceed 1,675°F., for a sufficient length of time to secure a case 
of from 0.02 to 0.04 in. deep. The pins are then allowed to cool 
slowly from the carbonizing heat, after which the hole is finish- 
machined and the pin cut to length. The finish heat treatment 
of the piston pin consisted in quenching in oil from a temperature 
of from 1,525 to 1,575°F. to refine the grain of core properly and 
then quenching in oil at a temperature of from 1,340 to 1,380°F. 
to refine and harden the grain of the case properly, as well as to 
secure proper hardness of core. After this quenching, all piston 
pins are tempered in oil at a temperature of from 375 to 400 °F. 
A 100 per cent inspection for scleroscope hardness of the case and 
the core was made, and no failures were ever recorded when the 
above material and heat treatment was used. 

APPLICATION TO THE AUTOMOTIVE INDUSTRY 

The information given on the various parts of the Liberty 
engine applies with equal force to the corresponding parts in the 
construction of an automobile, truck or tractor. We recommend 
as first choice for carbon-steel screw-machine parts material 
produced by the basic open hearth process and having the follow- 
ing chemical composition; Carbon, 0.150 to 0.250 per cent; 
manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 maxi- 
mum per cent; sulphur, 0.075 to 0.150 per cent. 



58 THE WORKING OF STEEL 

This material is very uniform and is nearly as free cutting as 
bessemer screw stock. It is sufficiently uniform to be used for 
unimportant carburized parts, as well as for non-heat-treated 
screw-machine parts. A number of the large automobile manu- 
facturers are now specifying this material in preference to the 
regular bessemer grades. 

As second choice for carbon-steel screw-machine parts we recom- 
mend ordinary bessemer screw stock, purchased in accordance 
with S. A. E. specification No. 1114. The advantage of using No. 
1114 steel lies in the fact that the majority of warehouses carry 
standard sizes of this material in stock at all times. The disad- 
vantage of using this material is due to its lack of uniformity. 

The important criterion for transmission gears is resistance 
to wear. To secure proper resistance to wear a Brinell hardness 
of from 512 to 560 must be obtained. The material selected to 
obtain this hardness should be one which can be made most 
nearly uniform, will undergo forging operations the easiest, will 
be the hardest to overheat or burn, will machine best and will 
respond to a good commercial range of heat treatment. 

It is a well-known fact that the element chromium, when in 
the form of chromium carbide in alloy steel, offers the greatest 
resistance to wear of any combination yet developed. It is also 
a well-known fact that the element nickel in steel gives excellent 
shock-resisting properties as well as resistance to wear but not 
nearly as great a resistance to wear as chromium. It has been 
standard practice for a number of years for many manufacturers 
to use a high nickel-chromium steel for transmission gears. A 
typical nickel-chromium gear specification is as follows : Carbon, 
0.470 to 0.520 per cent; manganese, 0.500 to 0.800 per cent; 
phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum 
per cent; chromium, 0.700 to 0.950 per cent- 
There is no question but that a gear made from material of 
such an analysis will give excellent service. However, it is possi- 
ble to obtain the same quality of service and at the same time 
appreciably reduce the cost of the finished part. The gear steel 
specified is of the air-hardening type. It is extremely sensitive 
to secondary pipe, as well as seams, and is extremely diffiuclt to 
forge and very easy to overheat. The heat-treatment range is 
very wide, but the danger from quenching cracks is very great. 
In regard to the machineability, this material is the hardest to 
machine of any alloy steel known. 



APPLICATION OF LIBERTY ENGINE MATERIALS 59 

COMPOSITION OF TRANSMISSION-GEAR STEEL 

If the nickel content of this steel is eliminated, and the per- 
centage of chromium raised slightly, an ideal transmission-gear 
material is obtained. This would, therefore, be of the following 
composition: Carbon, 0.470 to 0.520 per cent; manganese, 0.500 
to 0.800 per cent; phosphorus, 0.040 maximum per cent; sulphur, 
0.045 maximum per cent; chromium, 0.800 to 1.100 per cent. 

The important criterion in connection with the use of this 
material is that the steel be properly deoxidized, either through 
the use of ferrovanadium or its equivalent. Approximately 
2,500 sets of transmission gears are being made daily from material 
of this analysis and are giving entirely satisfactory results in 
service. The heat treatment of the above material for trans- 
mission gears is as follows: "Normalize forgings at a temperature 
of from 1,550 to 1,600°F. Cool from this temperature to a tem- 
perature of 1,100°F. at the rate of 50° per hour. Cool from 
1,100°F., either in air or quench in water." 

Forgings so treated will show a Brinell hardness of from 177 to 
217, which is the proper range for the best machineability. The 
heat treatment of the finished gears consists of quenching in oil 
from a temperature of 1,500 to 1,540°F., followed by tempering 
in oil at a temperature of from 375 to 425°F. Gears so treated 
will show a Brinell hardness of from 512 to 560, or a scleroscope 
hardness of from 72 to 80. One tractor builder has placed in 
service 20,000 sets of gears of this type of material and has never 
had to replace a gear. Taking into consideration the fact that 
a tractor transmission is subjected to the worst possible service 
conditions, and that it is under high stress 90 per cent of the time, 
it seems inconceivable that any appreciable transmission trouble 
would be experienced when material of this type is used on an 
automobile, where the full load is applied not over 1 per cent of 
the time, or on trucks where the full load is applied not over 50 
per cent of the time. 

The gear hardness specified is necessary to reduce to a mini- 
mum the pitting or surface fatigue of the teeth. If gears having 
a Brinell hardness of over 560 are used, danger is encountered, 
due to low shock-resisting properties. If the Brinell hardness 
is under 512, trouble is experienced due to wear and surface 
fatigue of the teeth. 

For ring gears and pinions material of the following chemical 
composition is recommended: Carbon, 0.100 to 0.200 per cent; 



60 THE WORKING OF STEEL 

manganese, 0.350 to 0.650 per cent; phosphorus, 0.040 maximum 
per cent; sulphur, 0.045 maximum per cent; chromium, 0.550 
to 0.750 per cent; nickel, 0.400 to 0.600 per cent. 

Care should be taken to see that this material is properly 
deoxidized either by the use of ferro vanadium or its equivalent. 
The advantage of using a material of the above type lies in the 
fact that it will produce a satisfactory finished part with a very 
simple treatment. The heat treatment of ring gears and pinions 
is as follows: "Carburize at a temperature of from 1,650 to 
1,700°F. for a sufficient length of time to secure a depth of case 
of from \^2 to % 4 in., and quench directly from carburizing 
heat in oil. Reheat to a temperature of from 1,430 to 1,460°F. 
and quench in oil. Temper in oil at a temperature of from 375 
to 425°F. The final quenching operation on a ring gear should 
be made on a fixture similar to the Gleason press to reduce 
distortion to a minimum." 

One of the largest producers of ring gears and pinions in the 
automotive industry has been using this material and treatment 
for the last 2 years, and is of the opinion that he is now producing 
the highest quality product ever turned out by that plant. 

On some designs of automobiles a large amount of trouble 
is experienced with the driving pinion. If the material and heat 
treatment specified will not give satisfaction, rather than to 
change the design it is possible to use the following analysis 
material, which will raise the cost of the finished part but will 
give excellent service: Carbon, 0.100 to 0.200 per cent; manga- 
nese, 0.350 to 0.650 per cent; phosphorus, 0.040 maximum per 
cent; sulphur, 0.045 maximum per cent; nickel, 4.750 to 5.250 
per cent. 

The heat treatment of pinions produced from this material 
consists in carburizing at a temperature of from 1,600 to 1,650°F. 
for a sufficient length of -time to secure a depth of case from 3^2 
to %4 in. The pinions are then quenched in oil from a tempera- 
ture of 1,500 to 1,525°F. to refine the grain of the core and 
quenched in oil from a temperature of from 1,340 to 1,360°F. to 
refine and harden the case. The use of this material however, 
is recommended only in an emergency, as high-nickel steel is 
very susceptible to seams, secondary pipe and laminations. 

The main criterion on rear-axle and pinion shafts, steering 
knuckles and arms and parts of this general type is resistance to 
fatigue and torsion. The material recommended for parts of 



APPLICATION OF LIBERTY ENGINE MATERIALS 61 

this character is either S. A. E. No. 6135 or No. 3135 steel, 
which have the chemical composition given in Tables 9 and 7. 

HEAT TREATMENT OF AXLES 

Parts of this general type should be heat-treated to show the 
following minimum physical properties: Elastic limit, 115,000 
lb. per square inch; elongation in 2 in., 16 per cent; reduction of 
area, 50 per cent; Brinell hardness, 277 to 321. 

The heat treatment used to secure these physical properties 
consists in quenching from a temperature of from 1,520 to 1,540°F. 
in water and tempering at a temperature of from 975 to 1,025°F. 
Where the axle shaft is a forging, and in the case of steering- 
knuckles and arms, this heat treatment should be preceded by 
normalizing the forgings at a temperature of from 1,550 to 1,600°F. 
It will be noted that these physical properties correspond to those 
worked out for an ideal aviation engine crankshaft. If parts of 
this type are designed with proper sections, so that this range of 
physical properties can be used, the part in question will give 
maximum service. 

One of the most important developments during the Liberty 
engine program was the fact that it is not necessary to use a high- 
analysis alloy steel to secure a finished part which will give proper 
service. This fact should save the automotive industry millions 
of dollars on future production. 

If the proper authority be given the metallurgical engineer to 
govern the handling of the steel from the time it is purchased 
until it is assembled into finished product, mild-analysis steels 
can be used and the quality of the finished product guaranteed. 
It was only through the careful adherence to these fundamental 
principles that it was possible to produce 20,000 Liberty engines, 
which are considered to be the most highly stressed mechanism 
ever produced, without the failure of a single engine from defec- 
tive material or heat treatment. 

MAKING STEEL BALLS 

Steel balls are made from rods or coils according to size, stock 
less than %6 -m - comes in coils. Stock %-in. and larger 
curves in rods. Ball stock is designated in thousandths so that 
%-in. rods are known as 0.625-in. stock. 



62 THE WORKING OF STEEL 

Steel for making balls of average size is made up of : 

Carbon 0. 95 to 1 . 05 per cent 

Silicon 0.20 to 0.35 per cent 

Manganese 0.30 to 0.45 per cent 

Chromium 0.35 to 0.45 per cent 

Sulphur and phosphorus not to exceed ... . 025 per cent 

For the larger sizes a typical analysis is : 

Carbon 1 . 02 per cent 

Silicon 0. 21 per cent 

Manganese . 40 per cent 

Chromium 0. 65 per cent 

Sulphur : . . . . 026 per cent 

Phosphorus : . 014 per cent 

Balls % in. and below are formed cold on upsetting or heading 
machines, the stock use is as follows: 

Table 14 — Sizes of Stock for Forming Balls on Header 



Diameter of 


Diameter of 


Diameter of 


Diameter of 


ball, inch 


stock inch 


ball, inch 


stock, inch 


H 


0.100 


He 


0.235 


%2 


0.120 


% 


0.275 


Vie 


0.145 


He 


0.320 


V32 


0.170 


y% 


0.365 


K 


0.190 


Vie 


0.395 


%2 


0.220 


% 


0.440 



For larger balls the blanks are hot-forged from straight bars. 
They are usually forged in multiples of four under a spring hammer 
and then separated by a suitable punching or shearing die in a 
press adjoining the hammer. The dimensions are: 



Diameter of ball, 
inch 


Diameter of die, 
inch 


Diameter of stock, 
inch 


H 

% 
l 


0.775 
0.905 
1.035 


0.625 
0.729 
0.823 



APPLICATION OF LIBERTY ENGINE MATERIALS 63 

Before hardening, the balls are annealed to relieve the stresses 
of forging and grinding, this being done by passing them through 
a revolving retort made of nichrome or other heat-resisting sub- 
stance. The annealing temperature is 1,300°F. 

The hardening temperature is from 1,425 to 1,475°F. according 
to size and composition of steel. Small balls, %q and under, 
are quenched in oil, the larger sizes in water. In some special 
cases brine is used. Quenching small balls in water is too great 
a shock as the small volume is cooled clear through almost 
instantly. The larger balls have metal enough to cool more 
slowly. 

Balls which are cooled in either water, or brine are boiled in 
water for 2 hr. to relieve internal stresses, after which the balls 
are finished by dry-grinding and oil-grinding. 

The ball makers have an interesting method of testing stock 
for seams which do not show in the rod or wire. The Hoover 
Steel Ball Company cut off pieces of rod or wire %6 m - l° n g and 
subject them to an end pressure of from 20,000 to 50,000 lb. 
A pressure of 20,000 lb. compresses the piece to % q in. and the 
50,000 lb. pressure to %2 in. This opens any seam which may 
exist but a solid bar shows no seam. 

Another method which has proved very successful is to pass 
the bar or rod to be tested through a solenoid electro-magnet. 
With suitable instruments it is claimed that this is an almost 
infallible test as the instruments show at once when a seam or 
flaw is present in the bar. 



CHAPTER V 

THE FORGING OF STEEL 

So much depends upon the forging of steel that it must be 
carefully considered. The main points are the heating to the 
proper temperature and the use of a hammer of the right size for 
the work to be forged. The bar of stock from which a forging was 
made may have had a fairly good structure, but if the shock of 
the falling die struck this bar of stock when at a temperature 
lower than the critical, its structure would become distorted, 
some of the crystals broken down and others reformed. If the 
temperature of the bar, however, was above the critical point, 
and the steel in an austenitic condition when the die struck it, 
the resulting steel will be a fairly uniform formation of aus- 
tenite crystals. Although the original structure will have been 
changed, the forged piece will still have the characteristic aus- 
tenite. Thus it is seen that the steel must be worked at the 
proper temperature. 

Steel Worked in Austenitic Stage. — As a general rule steel 
should be worked when it is in the austenitic stage. It is then 
sure to keep a uniform structure because the carbon is in solid 
solution with the iron and is therefore distributed uniformly 
throughout the metal. If it is worked below the critical point, 
the carbon has begun to stratify and form different combinations 
and carbides with the result that uniformity is not apt to result. 
Just as soon as the temperature begins to fall below the critical 
point the austenite begins to break up into ferrite and cementite. 
If the carbon content of the steel is high, cementite will result, 
and if it is low the greater part will be composed of ferrite. 

By working the steel well above the critical temperature the 
size of the austenite crystals is kept small and although on cooling 
the austenite crystals will not remain in that form if they are 
finely divided, the size of the grains of the final result will be 
much smaller and hence a more uniform structure will result. 
A final steel will be composed of pearlite; ferrite and pearlite; or 
cementite and pearlite, according to the carbon content. The 
higher the carbon content the greater percentage of cementite, 

64 



THE FORGING OF STEEL 65 

and therefore the harder the steel. It can always be remembered 
that the cause of the great effect of carbon on steel is due to the 
fact that it only takes 1 per cent of carbon to form 15 per cent 
of cementite — the hard, brittle constituent of the high-carbon 
steel. 

The ultimate object is to secure a fine, uniform grain and this 
can be secured by not reheating the metal to too high a tempera- 
ture and by thoroughly rolling it or working it at a temperature 
well above its critical point. If this is correctly done the micro- 
photograph will show a fine, evenly distributed grain which, in 
the case of carbon steel, will be composed of ferrite and pearlite. 
The ferrite is light gray and the pearlite has a black, stratified 
appearance on the microphotograph; the percentage of carbon 
will determine the relative quantities of ferrite and pearlite, i.e., 
the lower the carbon, the more ferrite. 

Steel Can be Worked Cold. — Steel can be worked cold, as in 
the case of cold-rolled steel, but afterwards it must be annealed 
in order to remove the internal strains which have resulted from 
the cold working. The annealing must be done above the critical 
point, i.e., at which the steel has been again raised to the austen- 
itic condition where the iron carbide is in solution, and on cooling 
a complete re-crystallization results. In annealing steel care 
must be taken that the exterior surface does not become oxidized, 
owing to the tendency of the metal to absorb oxygen while hot. 
When the surface becomes oxidized scale forms which peels off 
under slight stresses. 

FORGING 

High-speed Steel. — Heat very slowly and carefully to from 
1,800 to 2,000°F. and forge thoroughly and uniformly. If the 
forging operation is prolonged do not continue forging the tool 
when the steel begins to stiffen under the hammer. Do not 
forge below 1,700°F. (a dark lemon or orange color). Reheat 
frequently rather than prolong the hammering at the low heats. 

After finishing the forging allow the tool to cool as slowly as 
possible in lime or dry ashes; avoid placing the tool on the damp 
ground or in a draught of air. Use a good clean fire for heating. 
Do not allow the tool to soak at the forging heat. Do not heat 
any more of the tool than is necessary in order to forge it to the 
desired shape. 

Carbon Tool Steel. — Heat to a bright red, about 1,500 to 
1,550°F. Do not hammer steel when it cools down to a dark 

5 



66 THE WORKING OF STEEL 

cherry red, or just below its hardening point, as this creates 
surface cracks. 

Oil -hardening Steel. — Heat slowly and uniformly to 1,450°F. 
and forge thoroughly. Do not under any circumstances at- 
tempt to harden at the forging heat. After cooling from forging 
reheat to about 1,450°F. and cool slowly so as to remove forging 
strains. 

Chrome -nickel Steel. — Forging heat of chrome-nickel steel 
depends very largely on the percentage of each element con- 
tained in the steel. Steel containing from 3^ to 1 per cent chrome 
and from 1^ to 3^ per cent nickel, with a carbon content equal 
to the chromium, should be heated very slowly and uniformly 
to approximately 1,600°F., or salmon color. After forging, 
reheat the steel to about 1,450° and cool slowly so as to remove 
forging strains. Do not attempt to harden the steel before such 
annealing. 

A great deal of steel is constantly being spoiled by carelessness 
in the forging operation. The billets may be perfectly sound, 
but even if the steel is heated to a good forging heat, and is 
hammered after the outside surface becomes cold, a poor forging 
results. For, while the center of steel remained at the forging 
heat, hammering simply cooled the steel away from the center, 
opening the steel and making a bad pipe. 

Steel which is heated quickly and forging begun before uni- 
form heat has penetrated to its center is shocked by hammer 
blows. This opens up seams because the cooler central portion 
was not able to flow with the hot metal surrounding it. Uni- 
form heating is absolutely necessary for the best results. 

Figure 14 shows a sound forging. The bars in Fig. 15 were 
burst by improper forging, while the die, Fig. 16, burst from a 
piped center. 

Figure 17 shows a piece forged with a hammer too light for the 
size of the work. This gives an appearance similar to case- 
hardening, the refining effect of the blows reaching but a short 
distance from the surface. 

The size of hammers for forgings is important and the following- 
data from the "American Machinists Handbook" is of value as a 
general guide. 

While it is impossible to accurately rate the capacity of steam 
hammers with respect to the size of work they should handle, on 
account of the greatly varying conditions, a few notes from the 



THE FORGING OF STEEL 



67 



experience of the Bement works of the Niles-Bement-Pond 
Company will be of service. 

For making an occasional forging of a given size, a smaller 
hammer may be used than if we are manufacturing this same 




Fig. 14. — A sound forging. 




Fig. 15. — Burst from improper forging. 



piece in large quantities. If we have a 6-in. piece to forge, such 
as a pinion or a short shaft, a hammer of about 1,100-lb. capacity 
would answer very nicely. But should the general work be as 



68 



THE WORKING OF STEEL 



large as this, it would be very much better to use a 1,500-lb. 
hammer. If, on the other hand, we wish to forge 6-in. axles 
economically, it would be necessary to use a 7,000- or 8,000-lb. 
hammer. The following table will be found convenient for 




Fig. 16. — Burst from a piped center. 




Fig. 17. — Result of using too light a hammer. 



reference for the proper size of hammer to be used on different 
classes of general blacksmith work, although it will be understood 
that it is necessary to modify these to suit conditions, as has 
already been indicated. 



THE FORGING OF STEEL 



69 



Diameter of stock Size of hammer 

Sy 2 in 250 to 350 1b. 

4 in 350 to 600 1b. 

AY 2 in 600 to 800 1b. 

5 in 800 to 1,000 lb. 

6 in . 1,100 to 1,500 1b. 

Steam hammers are always rated by the weight of the ram, and 
the attached parts, which include the piston and rod, nothing 
being added on account of the steam pressure behind the piston. 
This makes it a little difficult to compare them with plain drop or 
tilting hammers, which are also rated in the same way. 




ABC 
Fig. 18. — Good and bad forgings. 

Steam hammers are usually operated at pressures varying from 
75 to 100 lb. of steam per square inch, and may also be operated 
by compressed air at about the same pressures. It is cheaper, 
however, in the case of compressed air to use pressures from 60 to 
80 lb. instead of going higher. 

Forgings must, however, be made from sound billets if satis- 
factory results are to be secured. Figure 18 shows three cross- 
sections of which A is sound, B is badly piped and C is worthless. 

PLANT FOR FORGING RIFLE BARRELS 

The forging of rifle barrels in large quantities and heat-treating 
them to meet the specifications demanded by some of the foreign 
governments led Wheelock, Lovejoy & Company to establish a 
complete plant for this purpose in connection with their ware- 
house in Cambridge, Mass. This plant, designed and constructed 



70 



THE WORKING OF STEEL 




THE FORGING OF STEEL 



71 



by their chief engineer, K. A. Juthe, had many interesting fea- 
tures. Many features of this plant can be modified for other 
classes of work. 

The stock, which came in bars of mill length, was cut off so 
as to make a barrel with the proper allowances for trimming 
(Fig. 19). They then pass to the forging or upsetting press in 
the adjoining room. This press, which is shown in more detail 
in Fig. 20 handled the barrels from all the heating furnaces 
shown. The men changed work at frequent intervals, to avoid 
excessive fatigue. 




iting furnace. 



Then the barrels were reheated in the continuous furnace, 
shown in Fig. 21, and straightened before being tested. 

The barrels were next tested for straightness. After the heat- 
treating, the ends are ground, a spot ground on the enlarged end 
and each barrel tested on a Brinell machine. The pressure used 
is 3,000 kg., or 6,614 lb., and a depression of 3.9 mm., or No. 241, 
is usually secured. 

The heat-treating of the rifle blanks covered four separate 
operations: (1) Heating and soaking the steel above the critical 
temperature and quenching in oil to harden the steel through to 
the center; (2) reheating for drawing of temper for the purpose 



72 THE WORKING OF STEEL 

of meeting the physical specifications; (3) reheating to meet 
the machineability test for production purposes; and (4) reheating 
to straighten the blanks while hot. 

A short explanation of the necessity for the many heats may 
be interesting. For the first heat, the blanks were slowly 
brought to the required heat, which is about 150°F. above the 
critical temperature. They are then soaked at a high heat for 
about 1 hr. before quenching. The purpose of this treatment is 
to eliminate any rolling or heat stresses that might be in the bars 
from mill operations; also to insure a thorough even heat through 
a cross-section of the steel. This heat also causes blanks with 
seams or slight flaws to open up in quenching, making detection 
of defective blanks very easy. 

The quenching oil was kept at a constant temperature of 
100°F., to avoid subjecting the steel to shocks, thereby causing 
surface cracks. The drawing of temper was the most critical 
operation and was kept within a 10° fluctuation. The degree of 
heat necessary depends entirely on the analysis of the steel, there 
being a certain variation in the different heats of steel as received 
from the mill. 

MACHINEABILITY 

Reheating for machineability was done at 100° less than the 
drawing temperature, but the time of soaking is more than double. 
After both drawing and reheating, the blanks were buried in 
lime where they remain, out of contact with the air, until their 
temperature had dropped to that of the workroom. 

For straightening, the barrels were heated to from 900 to 
1,000°F. in an automatic furnace 25 ft. long, this operation 
taking about 2 hr. The purpose of hot straightening was to 
prevent any stresses being put into the blanks, so that after 
rough-turning, drilling or rifling operations they would not have 
a tendency to spring back to shape as left by the quenching 
bath. 

A method that produces an even better machining rifle blank, 
which practically stays straight through the different machining 
operations, was to rough-turn the blanks, then subject them to a 
heat of practically 1,000° for 4 hr. Production throughout the 
different operations is materially increased, with practically no 
straightening being from drilling, reaming, finish-turning or 
rifling operations. 



THE FORGING OF STEEL 



73 




74 



THE WORKING OF STEEL 



This method was tested out by one of the largest manufacturers 
and proved to be the best way to eliminate a very expensive 
finished gun-barrel straightening process. 

The heat-treating required a large amount of cooling oil, and 
the problem of keeping this at the proper temperature required 
considerable study. The result was the cooling plant on the 
roof, as shown in Figs. 22, 23 and 24. The first two illustrations 
show the plant as it appeared complete. Figure 24 shows how 
the oil was handled in what is sometimes called the ebulator 
system. The oil was pumped up from the cooling tanks through 
the pipe A to the tank B. From here it ran down onto the 







^- 5' _^-, 

•SWaI" FrnmMI 



«"AV from Oil 

%%~ ' Pump 

|* 

Fig. 24. — Details of the cooler. 




breakers or separators C, which break the oil up into fine particles 
that are caught by the fans D. The spray is blown up into the 
cooling tower E, which contains banks of cooling pipes, as can be 
seen, as well as baffles F. The spray collects on the cool pipes 
and forms drops, which fall on the curved plates G and run back 
to the oil-storage tank below ground. 

The water for this cooling was pumped from 10 artesian wells 
at the rate of 60 gal. per minute and cooled 90 gal. of oil per 
minute, lowering the temperature from 130 or 140 to 100°F. 
The water as it came from the wells averaged around 52°F. The 
motor was of a 7^-hp. variable-speed type with a range of from 
700 to 1,200 r.p.m., which could be varied to suit the amount 
of oil to be cooled. The plant handled 300 gal. of oil per minute. 



CHAPTER VI 

ANNEALING 

There is no nrystery or secret about the proper annealing of 
different steels, but in order to secure the best results it is abso- 
lutely necessary for the operator to know the kind of steel which 
is to be annealed. The annealing of steel is primarily done for 
one of three' specific purposes: To soften for machining purposes; 
to change the physical properties, largely to increase ductility; or 
to release strains caused b}~ rolling or forging. 

Proper annealing means the heating of the steel slowly and 
uniformly to the right temperature, the holding of the tempera- 
ture for a given period and the gradual cooling to normal tem- 
perature. The proper temperature depends on the kind of 
steel, and the suggestions of the maker of the special steel being 
used should be carefully followed. For carbon steel the tem- 
peratures recommended for annealing vary from 1,200 to 1,450°F. 
This temperature need not be long continued. The steel should 
be cooled in hot sand, lime or ashes. If heated in the open forge 
the steel should be buried in the cooling material as quickly as 
possible, not allowing it to remain in the open air any longer than 
absolutely necessary. Best results, however, are secured when 
the fire does not come in direct contact with the steel. 

Good results are obtained by packing the steel in iron boxes or 
tubes, much as for case-hardening or carbonizing, using the same 
materials. They do not require separation for annealing, 
however. Do not remove from boxes until cold. 

Steel to be annealed may be classified into four different groups, 
each of which must be treated according to the elements con- 
tained in its particular class, and different methods are therefore 
necessary to bring about the desired result. The classifications 
are as follows: High-speed steel, alio}'' steel, tool or crucible 
steel, and high-carbon machinery steel. 

ANNEALING OF HIGH-SPEED STEEL 

For annealing high-speed steel, some makers recommend using 
ground mica, charcoal, lime, fine dry ashes or lake sand as a 
packing in the annealing boxes. Mixtures of one part charcoal, 



76 THE WORKING OF STEEL 

one part lime and three parts of sand are also suggested, or two 
parts of ashes may be substituted for the one part of lime. 

To bring about the softest structure or machineability of high- 
speed steel, it should be packed in charcoal in boxes or pipes, 
carefully sealed at all points, so that no gases will escape or air 
be admitted. It should be heated slowly to not less than 1,450°F. 
and the steel must not be removed from its packing until it is 
cool. Slow heating means that the high heat must have pene- 
trated to the very core of the steel. 

When the steel is heated clear through it has been in the fur- 
nace long enough. If the steel can remain in the furnace and cool 
down with it, there will be no danger of air blasts or sudden or 
uneven cooling. If not, remove the box and cover quickly with 
dry ashes, sand or lime until it becomes cold. 

Too high a heat or maintaining the heat for too long a period, 
produces a harsh, coarse grain and greatly increases the liability 
to crack in hardening. It also reduces the strength and tough- 
ness of the steel. 

Steel which is to be used for making tools with teeth, such as 
taps, reamers and milling cutters, should not be annealed too 
much. When the steel is too soft it is more apt to tear in cutting 
and makes it more difficult to cut a smooth thread or other 
surface. Moderate annealing is found best for tools of this 
kind. 

TOOL OR CRUCIBLE STEEL 

Crucible steel can be annealed either in muffled furnace or by 
being packed. Packing is by far the most satisfactory method as 
it prevents scaling, local hard spots, uneven annealing, or violent 
changes in shape. It should be brought up slowly to just above 
its calescent or hardening temperature. The operator must 
know before setting his heats the temperature at which the differ- 
ent carbon content steels are hardened. The higher the carbon 
contents the lower is the hardening heat, but this should in no 
case be less than 1,400°F. 

ANNEALING ALLOY STEEL 

The term alloy steel from the steel maker's point of view, refers 
largely to nickel and chrome steel or a combination of both. 
These steels are manufactured very largely by the open hearth 
process. Although chromium steels are also a crucible product, 
it is next to impossible to give proper directions for the proper 



ANNEALING 77 

annealing of alloy steel unless the four principal elements con- 
tained in such steels are known to the operator. These four 
elements are: carbon, manganese, chromium and nickel. Each 
element is a deciding factor in hardening such steel and therefore 
the proper annealing is of great importance. In annealing this 
steel, however, not much importance need be laid to the carbon 
content. The length of time or the temperature is in direct 
proportion to its chromium and nickel contents. The chromium 
content decides the degree of temperature and the amount of 
nickel decides the time required for thorough penetration and 
proper changing or mixing of the elements. A steel with a content 
of 20 points each of chromium and nickel, and from 60 to 90 
points of manganese, requires not less than 1,350°F. 

HIGH-CARBON MACHINERY STEEL 

The carbon contents of this steel is above 30 points and is 
hardly ever above 100 points or 1 per cent. Annealing such 
steel is generally one of quantity production and does not require 
the care that the other steels need because it is very largely a 
much cheaper product and a great deal of material is generally 
removed from the outside surface. 

The purpose for which this steel is annea^d is a deciding- 
factor as to what heat to give it. If it is for machineability only, 
the steel requires to be brought up slowly to not less than 1,300°F. 
and then slowly cooled in the furnace or ash pit. It must be 
thoroughly covered so that there will be no access of cool air. 
If the annealing is to increase ductility or to affect some other 
physical property of the steel, it should be slowly heated to 
between 1,100 and 1,200°F. and kept at this heat for a length of 
time necessary for a thorough penetration to the core, after which 
it can be removed and put in an ash pit or covered with lime. 
If the annealing is just to relieve strains, slow heating is not 
necessary, but the steel must be brought up to a temperature 
not much less than a forging or rolling heat and gradually cooled. 
Covering in this case is only necessary in steel of a carbon content 
of more than 40 points. 

ANNEALING IN BONE ' 

Steel and cast iron may both be annealed in granulated bone. 
Pack the work the same as for case-hardening except that it is 
not necessary to keep the pieces away from each other. Pack 



78 THE WORKING OF STEEL 

with bone that has been used until it is nearly white. Heat as 
hot as necessary for the steel and let the furnace cool down. If 
the boxes are removed from furnace while still warm, cover 
boxes and all in warm ashes or sand, air slaked lime or old, 
burned bone to retain heat as long as possible. Do not remove 
work from boxes until cold. 

ANNEALING OF RIFLE COMPONENTS AT SPRINGFIELD ARMORY 

In general, all forgings of the components of the arms manu- 
factured at the Armory and all forgings for other ordnance estab- 
lishments are packed in charcoal, lime or suitable material and 
annealed before being transferred from the forge shop. 

Except in special cases, all annealing will be done in annealing 
pots of appropriate size. One fire end of a thermo-couple is 
inserted in the center of the annealing pot nearest the middle of 
the furnace and another in the furnace outside of but near the 
annealing pots. 

The temperatures used in annealing carbon steel components 
of the various classes used at the Armory vary from 800°C. to 
880°C. or 1,475 to 1,615°F. 

The fuel is shut off from the annealing furnace gradually as 
the temperature of the pot approaches the prescribed annealing 
temperature so as to prevent heating beyond that temperature. 

The forgings of the rifle barrel and the pistol barrel are excep- 
tions to the above general rule. These forgings will be packed 
in lime and allowed to cool slowly from the residual heat after 
forging. 



CHAPTER VII 

CASE-HARDENING OR SURFACE-CARBURIZING 

Carburizing, commonly called case-hardening, is the art of 
producing a tool-steel surface, or case, upon a machinery steel 
article. Wrenches, locomotive link motions, gun mechanisms, 
balls and ball races, automobile gears and many other devices 
are thereby given a high-carbon case capable of assuming extreme 
hardness, while the interior body of metal, the core, remains soft 
and tough. 

The simplest method is to heat the piece to be hardened to a 
bright red, dip it in cyanide of potassium (or cover it by sprin- 
kling the cyanide over it), keep it hot until the cyanide covers it 
thoroughly, and quench in water. This converts the outer skin 
into steel and hardens this skin but leaves the center soft. The 
hard surface or "case" varies in thickness according to the size 
of the piece, the materials used and the length of time which the 
piece remains at the carburizing temperature. Cyanide case- 
hardening is used only where a light or thin skin is sufficient. It 
gives a thickness of about 0.002 in. The penetration of carbon- 
izing will be given later. 

In some cases of cyanide carburizing, the piece is heated in 
cyanide to the desired temperature and then quenched. For a 
thicker case the steel is packed in carbon materials of various 
kinds such as burnt leather scraps, charcoal, granulated bone or 
some of the many carbonizing compounds. 

Machined or forged steel parts are packed with case-hardening 
material in metal boxes and subjected to a red heat. Under 
such conditions, carbon is absorbed by the steel surfaces, and a 
carburized case is produced capable of responding to ordinary 
hardening and tempering operations, the core meanwhile retain- 
ing its original softness and toughness. 

Such case-hardened parts are stronger, cheaper, and more 
serviceable than similar parts made of tool steel. The tough 
core resists breakage by shock. The hardened case resists 
wear from friction. The low cost of material, the ease of manu- 
facture, and the lessened breakage in quenching all serve to 
promote cheap production. 

79 



80 



THE WORKING OF STEEL 



For successful carburizing, the following points should be 
carefully observed: 

The utmost care should be used in the selection of pots for 
carburizing; they should be as free as possible from both scaling 
and warping. These two requirements eliminate the cast iron 
pot, although many are used, thus leaving us to select from 




Fig. 25. 



Fig. 26. 



-• <§ • © #j 

•[©"©liiGL: 






o[o^if- 



4= 



fl=* 




Fig. 27. 



Fig. 28. 



Figs. 25 to 28. — Case-hardening or carburizing boxes. 




D> 



Fig. 29. — A lid that is easily luted. 



malleable castings, wrought iron, cast steel, and special alloys, 
such as nichrome or silchrome. If first cost is not important, 
it will prove cheaper in the end to use pots of some special alloy. 
The pots should be standardized to suit the product. Pots 
should be made as small as possible in width, and space gained 
by increasing the height; for it takes about 1% hr. to heatthe 



CASE-HARDENING OR SURFACE-CARBONIZING 81 

average small pot of 4 in. in width, between 3 and 4 hr. to heat 
to the center of an 8-in. box, and 5 to 6 hr. to heat to the center 
of a 12-in. box; and the longer the time required to heat to the 
center, the more uneven the carburizing. 

The work is packed in the box surrounded by materials which 
will give up carbon when heated. It must be packed so that 
each piece is separate from the others and does not touch the 
box, with a sufficient amount of carburizing material surrounding 
each. Figures 25 to 29 show the kind of boxes used and the way 
the work should be packed. Figure 29 shows a later type of box 
in which the edges can be easily luted. Figure 28 shows how 
test wires are used to determine the depth of case. Figure 26 
shows the minimum clearance which should be used in packing 
and Fig. 27 the way in which the outer pieces receive the heat 
first and likewise take up the carbon before those in the center. 
This is why a slow, soaking heat is necessary in handling large 
quantities of work, so as to allow the heat and carbon to soak in 
equally. 

The temperature depends upon the carbon contents of the 
steel being treated and the length of time upon the depth of case 
required. The temperature range is about as follows: 



Per cent carbon 


"Points 


" of carbon 


Degrei 


3S Fahi 


0.10 






10 




1,616 


0.20 






20 




1,562 


0.30 






30 




1,535 


0.40 






40 




1,508 


0.50 






50 




1,492 


0.60 






60 




1,481 


0.70 






70 




1,476 


. 80 to 1 


5 


80 to 150 




1,472 



The most important thing in carburizing is the human element. 
Most careful vigilance should be kept when packing and unpack- 
ing, and the operator should be instructed in the necessity for 
clean compound free from scale, moisture, fire clay, sand, floor 
sweepings, etc. From just such causes, many a good carburizer 
has been unjustly condemned. It is essential with most carbu- 
rizers to use about 25 to 50 per cent of used material, in order to 
prevent undue shrinking during heating; therefore the necessity 
of properly screening used material and carefully inspecting it 
for foreign substances before it is used again. It is right here 
that the greatest carelessness is generally encountered. 

6 



82 THE WORKING OF STEEL 

Don't pack the work to be carburized too closely; leave at 
least 1 in. from the bottom, % in. from the sides, and 1 in. from 
the top of pots, and for a 6-hr. run, have the pieces at least % in. 
apart. This gives the heat a chance to thoroughly permeate 
the pot, and the carburizing material a chance to shrink without 
allowing carburized pieces to touch and cause soft spots. 

Good case-hardening pots and annealing tubes can be made 
from the desired size of wrought iron pipe. The ends are capped 
or welded, and a slot is cut in the side of the pot, equal to one 
quarter of its circumference, and about % of its length. Another 
piece of the same diameter pipe cut lengthwise into thirds forms 
a cover for this pot. We then have a cheap, substantial pot, 
non-warping, with a minimum tendency to scale. This idea is 
especially adaptable when long, narrow pots are desired, and 
works out very successfully. 

When pots are packed and the carburizer thoroughly tamped 
down, the covers of the pot are put on and sealed with fire clay 
which has a little salt mixed into it. The more perfect the seal 
the more we can get out of the carburizer. The rates of pene- 
tration depend on temperature and the presence of proper gas 
in the required volume. Any pressure we can cause will, of course, 
have a tendency to increase the rate of penetration. 

If you have a wide furnace, do not load it full at one time. 
Put one-half your load in first, in the center of the furnace, and 
heat until pots show a low red, about 1,325 to 1,350°F. Then 
fill the furnace by putting the cold pots on the outside or, the 
section nearest the source of heat. This will give the work in 
the slowest portion of the furnace a chance to come to heat at the 
same time as the pots that are nearest the sources of heat. 

To obtain an even heating of the pots and lessen their tendency 
to warp and scale, and to cause the contents of the furnace to 
heat up evenly, we should use a reducing fire and fill the heating 
chamber with flame. This can be accomplished by partially 
closing the waste gas vents and reducing slightly the amount of 
air used by the burners. A short flame will then be noticed 
issuing from the partially closed vents. Thus, while maintain- 
ing the temperature of the heating chamber, we will have a lower 
temperature in the combustion chamber, which will naturally 
increase its longevity. 

It is always advisable to allow work to cool in the pots. This 
saves compound, and causes a more gradual diffusion of the carbon 



CASE-HARDENING OR SURFACE-CARBONIZING 83 

between the case and the core, and is very desirable condition, 
inasmuch as abrupt cases are inclined to chip out. 

The most satisfactory steel to carburize contains between 
0.10 and 0.20 per cent carbon, less than 0.35 per cent manganese, 
less than 0.04 per cent phosphorus and sulphur, and low silicon. 
But steel of this composition does not seem to satisfy our pro- 
gressive engineers, and many alloy steels are now on the market, 
these, although more or less difficult to machine, give when 
carburized the various qualities demanded, such as a very hard 
case, very tough core, or very hard case and tough core. How- 
ever, the additional elements also have a great effect both on the 
rate of penetration during the carburizing operation, and on the 
final treatment, consequently such alloy steels require very care- 
ful supervision during the entire heat treating operations. 

RATE OF ABSORPTION 

According to Guillet, the absorption of carbon is favored by 
those special elements which exist as double carbides in steel. 
For example, manganese exists as manganese carbide in combina- 
tion with the iron carbide. The elements that favor the 
absorption of carbon are: manganese, tungsten, chromium and 
molybdenum those opposing it, nickel, silicon, and aluminum. 
Guillet has worked out the effect of the different elements on the 
rate of penetration in comparison with steel that absorbed carbon 
at a given temperature, at an average rate of 0.035 in. per hour. 

His tables show that the following elements require an in- 
creased time of exposure to the carburizing material in order to 
obtain the same depth of penetration as with simple steel: 

When steel contains Increased time of exposure 

2 . per cent nickel 28 per cent 

7.0 per cent nickel. . 30 per cent 

1 . per cent titanium 12 per cent 

2 . per cent titanium 28 per cent 

0.5 per cent silicon 50 per cent 

1 . per cent silicon 80 per cent 

2.0 per cent silicon 122 per cent 

5 . per cent silicon No penetration 

1 . per cent aluminum 122 per cent 

2 . per cent aluminum 350 per cent 

The following elements seem to assist the rate of penetration of 
carbon, and the carburizing time may therfore be reduced as 
follows : 



84 THE WORKING OF STEEL 

When steel contains Decreased time of exposure 

0.5 per cent manganese 18 per cent 

1 . per cent manganese 25 per cent 

1 . per cent chromium 10 per cent 

2.0 per cent chromium IS per cent 

. 5 per cent tungsten 

1 . per cent tungsten 

2 . per cent tungsten 25 per cent 

1 . per cent molybdenum 

2.0 per cent molybdenum 18 per cent 

The temperature at which carburization is accomplished is a 
very important factor. Hence the necessity for a reliable pyro- 
meter, located so as to give the temperature just below the tops of 
the pots. It must be remembered, however, that the pyrometer 
gives the temperature of only one spot, and is therefore only an 
aid to the operator, who must use his eyes for successful results. 

The carbon content of the case generally is governed by the 
temperature of the carburization. It generally proves advisable 
to have the case contain between 0.90 per cent and 1.10 carbon; 
more carbon than this gives rise to excess free cementite or carbide 
of iron, which is detrimental, causing the case to be brittle and 
apt to chip. 

T. G. Selleck gives a very useful table of temperatures and the 
relative carbon contents of the case of steels carburized between 
4 and 6 hrs. using a good charcoal carburizer. This data is as 
follows : 

Table 15. — Carbon Content Obtained at Various Temperatures 

At 1,500°F., the surface carbon content will be 0.90 per cent 
At 1,600°F., the surface carbon content will be 1 . 00 per cent 
At 1,650°F., the surface carbon content will be 1 . 10 per cent 
At 1,700°F., the surface carbon content will be 1 .25 per cent 
At 1,750°F., the surface carbon content will be 1.40 per cent 
At 1,800°F., the surface carbon content will be 1 .75 per cent 

To this very valuable table, it seems best to add the following 
data, which we have used for a number of years. We do not 
know the name of its author, but it has proved very valuable, 
and seems to complete the above information. The table is self- 
explanatory, giving depth of penetration of the carbon of the case 
at different temperatures for different lengths of time: 



CASE-HARDENING OR SURFACE-CARBURIZING 



85, 



Penetration 



Temperature 



1,550 



1,650 



1,800 



Penetration after % nr - 
Penetration after 1 hr. . 
Penetration after 2 hr. . 
Penetration after 3 hr. . 
Penetration after 4 hr. . 
Penetration after 6 hr. . 



0.008 
0.018 
0.035 
0.045 
0.052 
0.056 
Penetration after 8 hr. 0. 062 



0.012 
0.026 
0.048 
0.055 
0.061 
0.075 
0.083 



0.030 
0.045 
0.060 
0.075 
0.092 
0.110 
0.130 



From the tables given, we may calculate with a fair degree of 
certainty the amount of carbon in the case, and its penetration. 
The facts can be very readily checked by an examination of 
samples with the microscope. 

CARBURIZING MATERIAL 

The simplest carburizing substance is pure carbon. It is also 
the most inefficient, but can be used if mixed with something that 
will evolve carbon monoxide or nitrogen gas on being heated. A 
great variety of materials is used in carburizing mixtures, a few 
of them being charcoal (both wood and bone), charred leather, 
crushed bone, horn, mixtures of charcoal and barium carbonate, 
coke and heavy oils, coke treated with alkaline carbonates, peat, 
charcoal mixed with common salt, saltpeter, resin, flour, potas- 
sium, bichromate, vegetable fibre, limestone, various seed husks, 
etc. 

H. L. Heathcote, on analyzing seventeen different carburizers, 
found that they contained the following ingredients: 

Per cent 

Moisture 2 . 68 to 26 . 17 

Oil 0.17 to 20.76 

Carbon (organic) 6 . 70 to 54 . 19 

Calcium phosphate 0.32 to 74. 75 

Calcium carbonate 1 . 20 to 11 . 57 

Barium carbonate nil to 42 . 00 

Zinc oxide nil to 14 . 50 

Silica nil to 8.14 

Sulphates (S0 3 ) trace to 3.45 

Sodium chloride nil to 7.88 

Sodium carbonate nil to 40.00 

Sulphides (S) nil to 2.80 



86 



THE WORKING OF STEEL 



Carburizing mixtures, though bought by weight, are used by 
volume, and the weight per cubic foot is a big factor in making a 
selection. A good mixture should be porous, so that the evolved 
gases, which should be generated at the proper temperature, may 
move freely around the steel objects being carburized; should be a 
good conductor of heat; should possess minimum shrinkage when 
used; and should be capable of being tamped down. 

Mr. Heathcote also claims that by " incorporating a little 
potassium carbonate with exhausted charcoal is found to restore 
at once its carburizing power and make it give up its carbon more 
readily than the original charcoal." The same is true when potas- 
sium hydrate or sodium carbonate is incorporated. 

QUENCHING 

It is generally considered good practice to quench from the 
pot, especially if the case is of any appreciable depth. The tex- 




Fig. 30. — Case-hardening depths. 

ture of the steel has been weakened by the prolonged high heat 
of carburizing, so that if we need a tough core, we must treat it 
above its critical range, which is about 1,600°F. for simple steel, 
but lower for manganese and nickel steels. Quenching is done 
in either water, oil, or air, depending upon the results desired. 
The steel is then very carefully reheated to refine the case, the 
temperature varying from 1,350 to 1,450°F., depending on 
whether the material is an alloy or a simple steel, and quenched 
in either water or oil. 

There are many possibilities yet to be developed with the car- 
burizing of alloy steels, which can produce a very tough, tenacious 



CASE-HARDENING OR SURFACE-CARBURIZING 



87 



austenitic case which becomes hard on cooling in air, and still 
retain a soft, pearlitic core. An austenitic case is not necessarily 
file hard, but has a very great resistance to abrasive wear. 

The more carbon a steel has to begin with the more slowly will 
it absorb carbon and the lower the temperature required. Low 
carbon steel of from 15 to 20 points is generally used and the 
carbon brought up to 80 or 85 points. Tool steels may be carbon- 
ized as high as 250 points but this is seldom if ever required. 

In addition to the carburizing materials given, a mixture of 40 
per cent of barium carbonate and 60 per cent charcoal gives much 
faster penetration than charcoal, bone or leather. The penetra- 
tion of this mixture on ordinary low-carbon steel is shown in Fig. 
30, over a range of from 2 to 12 hr. 

EFFECT OF DIFFERENT CARBURIZING MATERIAL 

Each of these different packing materials has a different effect 
upon the work in which it is heated. Charcoal by itself will give 



Fig. 31. 



Fig. 32. 



Fig. 33. 



Spent 




Fig. 35. 



Fig. 34. 



Figs. 31 to 35. 



a rather light case. Mixed with raw bone it will carburize more 
rapidly, and still more so if mixed with burnt bone. Raw bone 
and burnt bone, as may be inferred, are both quicker carbonizers 
than charcoal, but raw bone must never be used where the break- 
age of hardened edges is to be avoided, as it contains phosphorus 
and tends to make the piece brittle. Charred leather mixed with 
charcoal is a still faster material, and horns and hoofs exceed even 
this in speed; but these two compounds are restricted by their 
cost to use with high-grade articles, usually of tool or high-carbon 
steel, that are to be hardened locally — that is, "pack-hardened." 



88 THE WORKING OF STEEL 

Cyanide of potassium and prussiate of potash are also included 
in the list of carbonizing materials; but outside of carburizing 
by dipping into melted baths of these materials, their use is 
largely confined to local hardening of small surfaces, such as holes 
in dies and the like. 

One of the advantages of hardening by carburizing is the fact 
that you can arrange to leave part of the work soft and thus retain 
the toughness and strength of the original material. Figures 

31 to 35 show ways of doing this. The inside of the cup in Fig. 

32 is locally hardened, as illustrated in Fig. 32, "spent" or used 
bone being packed around the surfaces that are to be left soft, 
while cyanide of potassium is put around those which are desired 
hard. The threads of the nut in Fig. 33 are kept soft by carbur- 
izing the nut while upon a stud. The profile gage, Fig. 34, is 
made of high-carbon steel and is hardened on the inside by pack- 
ing with charred leather, but kept soft on the outside by surround- 
ing it with fireclay. The rivet stud shown in Fig. 35 is carburized 
while of its full diameter and then turned down to the size of the 
rivet end, thus cutting away the carburized surface. 

Pieces of this kind are of course not quenched and hardened 
in the carburizing heat, but are left in the box to cool, just as in 
box annealing, being reheated and quenched as a second operation. 
In fact, this is a good scheme to use for the majority of carburizing 
work of small and moderate size. Sometimes it is desired to 
harden a thin piece of sheet steel halfway through, retaining the 
soft portion as a backing for strength. Material is on the market 
with which one side of the steel can be treated; or copper-plating 
one side of it will answer the same purpose and prevent that side 
becoming carburized. 

QUENCHING THE WORK 

In some cases case-hardened work is quenched right from the 
box by dumping the whole contents into the quenching tank. 
It is common practice to leave a sieveor wire basket to catch the 
work, allowing the carburizing material to fall to the botom of 
the tank where it can be recovered later and used again as a part 
of a new mixture. For best results, however, the steel is allowed 
to cool down slowly in the box after which it is removed and 
hardened by heating and quenching the same as carbon steel of 
the same grade. It has absorbed sufficient carbon so that, in the 
outer portions at least, it is a high-carbon steel. 



CASE-HARDENING OR SURF AC E-CARBURI ZING 89 

After packing the work carefully in the boxes the lids are 
sealed or luted with fireclay to keep out any gases from the 
fire. The size of box should be proportioned to the work. 
The box should not be too large especially for light work that is 
run on a short heat. If it can be just large enough to allow the 
proper amount of material around it, the work is apt to be more 
satisfactory in every way. 

The first or carburizing heat toughens the core. The reheat- 
ing temperature, that is the heating for quenching, can usually 
be about 200° lower than the first heat. Large work may re- 
quire 25° to 50° more heat than small work to secure the same 
results. The effect of size is treated in detail on page 117. 

CASE-HARDENING CAST IRON 

It is claimed that cast iron can also be hardened on the surface 
but that as it does not add to its strength its uses are limited to 
such pieces as gages and templets. Experience indicates, how- 
ever^ that the iron casting must be made malleable by long and 
uniform heating before it can be hardened. When this is done 
the surface can be given a surface hardness by using the follow- 
ing formula: 

To 20 gal. of water add 1 pt. of oil of vitrol, 2 pk. of salt, 4 lb. of 
alum, Y^ lb. of yellow prussiate of potash, ^ lb. cyanide of pot- 
ash and 1 lb. of salt peter. This should be kept in a covered 
wooden barrel. 

The casting to be hardened should be heated to a cherry red 
and then plunged into this bath which hardens the surface. It 
is sometimes necessary to repeat the operation two or three 
times to get the surface sufficiently hard. 

THE QUENCHING TANK 

The quenching tank is an important feature of apparatus in 
case-hardening — possibly more so than in ordinary tempering. 
One reason for this is because of the large quantities of pieces 
usually dumped into the tank at a time. One cannot take time 
to separate the articles themselves from the case-hardening 
mixture, and the whole content of the box is droped into the 
bath in short order, as exposure to air of the heated work is fatal 
to results. Unless it is split up, it is likely to go to the bottom 
as a solid mass, in which case very few of the pieces are properly 
hardened. 



90 



THE WORKING OF STEEL 



A combination cooling tank is shown in Fig. 36. Water inlet 
and outlet pipes are shown and also a drain plug that enables the 
tank to be emptied when it is desired to clean out the spent car- 
burizing material from the bottom. A wire-bottomed tray, 
framed with angle iron, is arranged to slide into this tank from 
the top and rests upon angle irons screwed to the tank sides. 
Its function is to catch the pieces and prevent them from settling 
to the tank bottom, and it also makes it easy to remove a batch 
of work. A bottomless box of sheet steel is shown at C. This 




Fig. 36. — Combination cooling tank for case-hardening. 



fits into the wire-bottomed tray and has a number of rods or wires 
running across it, their purpose being to break up the mass of 
material as it comes from the carbonizing box. 

Below the wire-bottomed tray is a perforated cross-pipe that 
is connected with a compressed-air line. This is used when case- 
hardening for colors. The shop that has no air compressor may 
rig up a satisfactory equivalent in the shape of a low-pressure 
hand-operated air pump and a receiver tank, for it is not neces- 
sary to use high-pressure air for this purpose. When colors are 
desired on case-hardened work, the treatment in quenching is 



CASE-HARDENING OR SURFACE-CARBURIZING 



91 




Untreated Steel 



fine grained and lough, 
CUb 'to 020% Carbon 



.Case 30% to 90% Carbon 
■Case hard and brittle 



exactly the same as that previously described except that air is 
pumped through this pipe and keeps the water agitated. The 
addition of a slight amount of powdered cyanide of potassium 
to the packing material used for carburizing will produce stronger 
colors, and where this is the sole object, it is best to maintain 
the box at a dull-red heat. 

The old way of case-hardening was to dump the contents of 
the box at the end of the carburizing 
heat. Later study in the structure of 
steel thus treated has caused a change 
in this procedure, the use of automobiles 
and alloy steels probably hastening this Za t^^™^ 
result. The diagrams reproduced in 
Fig. 37 show why the heat treatment 
of case-hardened work is necessary. 
Starting at A with a close-grained and 
tough stock, such as ordinary machinery 
steel containing from 15 to 20 points of 
carbon, if such work is quenched on a 
carbonizing heat the result will be as 
shown at B. This gives a core that is 
coarse-grained and brittle and an outer 
case that is fine-grained and hard, but 
is likely to flake off, owing to the great 
difference in structure between it and 
the core. Reheating this work beyond 
the critical temperature of the core re- 
fines this core, closes the grain and makes 

it tough, but leaves the case Very brittle; ment f case-hardened work 

in fact, more so than it was before. 




sCasedO% to90% Carbon 

Case brjnie and 

"very hard 

Core fine grained and 
tough, 015%to 020% 
Carbon 



Reheated to refine the Core 



Reheated to l500Deg.F 
Quenched in Water 




Fig 



■Case S0%to90% Carbon 
-Case tough and hard 

Core fine grained and 
tough,/5%toZO% Carbon 

Reheated 
to toughen the Case 



Why heat treat- 



REF1NING THE GRAIN 

This is remedied by reheating the piece to a temperature 
slightly above the critical temperature of the case, this tempera- 
ture corresponding ordinarily to that of steel having a carbon 
content of 85 points. When this is again quenched, the tempera- 
ture, which has not been high enough to disturb the refined core, 
will have closed the grain of the case and toughened it. So, 
instead of but one heat and one quenching for this class of work, 
we have three of each, although it is quite possible and often 
profitable to omit the quenching after carburizing and allow the 



92 THE WORKING OF STEEL 

piece or pieces and the case-carburizing box to cool together, as 
in annealing. Sometimes another heat treatment is added to 
the foregoing, for the purpose of letting down the hardness of the 
case and giving it additional toughness by heating to a tempera- 
ture between 300° and 500°. Usually this is done in an oil 
bath. After this the piece is allowed to cool. 

It is possible to harden the surface of tool steel extremely 
hard and yet leave its inner core soft and tough for strength, by 
a process similar to case-hardening and known as "pack-harden- 
ing." It consists in using tool steel of carbon contents ranging 
from 60 to 80 points, packing this in a box with charred leather 
mixed with wood charcoal and heating at a low-red heat for 2 or 
3 hr., thus raising the carbon content of the exterior of the 
piece. The article when quenched in an oil bath will have an 
extremely hard exterior and tough core. It is a good scheme for 
tools that must be hard and yet strong enough to stand abuse. 
Raw bone is never used as a packing for this class of work, as it 
makes the cutting edges brittle. 

CASE-HARDENING TREATMENTS FOR VARIOUS STEELS 

Plain water, salt water and linseed oil are the three most 
common quenching materials for case-hardening. Water is 
used for ordinary work, salt water for work which must be 
extremely hard on the surface, and oil for work in which tough- 
ness is the main consideration. The higher the carbon of the 
case, the less sudden need the quenching action take hold of the 
piece; in fact, experience in case-hardening work gives a great 
many combinations of quenching baths of these three materials, 
depending on their temperatures. Thin work, highly carbonized, 
which would fly to pieces under the slightest blow if quenched 
in water or brine, is made strong and tough by properly quenching 
in slightly heated oil. It is impossible to give any rules for 
the temperature of this work, so much depending on the size 
and design of the piece; but it is not a difficult matter to try 
three or four pieces by different methods and determine what is 
needed for best results. 

The alloy steels are all susceptible of case-hardening treat- 
ment; in fact, this is one of the most important heat treatments 
for such steels in the automobile industry. Nickel steel carbu- 
rizes more slowly than common steel, the nickel seeming to have 
the effect of slowing down the rate of penetration. There is no 



CASE-HARDENING OR SURFACE-CARBURIZING 93 

cloud without its silver lining, however, and to offset this retar- 
dation, a single treatment is often sufficient for nickel steel; for 
the core is not coarsened as much as low-carbon machinery steel 
and thus ordinary work may be quenched on the carburizing 
heat. Steel containing from 3 to 3.5 per cent of nickel is carbu- 
rized between 1,300 and 1,400°F. Nickel steel containing less 
than 25 points of carbon, with this same percentage of nickel, may 
be case-hardened by cooling in air instead of quenching. 

Chrome-nickel steel may be case-hardened similarly to the 
method just described for nickel steel, but double treatment 
gives better results and is used for high-grade work. The 
carburizing temperature is the same, between 1,300 and 1,400°F., 
the second treatment consisting of reheating to 1,400° and then 
quenching in boiling salt water, which gives a hard surface and 
at the same time prevents distortion of the piece. The core of 
chrome-nickel case-hardened steel, like that of nickel steel, is 
not coarsened excessively by the first heat treatment, and 
therefore a single heating and quenching will suffice for ordinary 
work. 

CARBURIZING BY GAS 

The process of carburizing by gas consists of having a slowly 
revolving, properly heated, cylindrical retort into which carburiz- 
ing gas is injected under pressure. The volatile carbon in the 
gas is easily absorbed, fresh gas being admitted and the spent 
gases are vented to insure the greatest speed in carbonizing. 
The work is constantly and uniformly exposed to an atmosphere 
of carbon instead of the solid carbons which turn to ash. The 
absorption of carbon begins as soon as the work heats sufficiently. 

Originally this process required a gas generator but this has 
been obviated in later machines. The gas consists of carbon 
vapor derived from petroleum, diluted by a neutral gas in such 
proportion that the carbon is supplied to the work as fast as it 
can be absorbed without forming obstructive deposits. 

PREVENTING CARBURIZING BY COPPER-PLATING 

Copper-plating has been found effective and must have a thick- 
ness of 0.0005 in. Less than this does not give a continuous coat- 
ing. The plating bath used had a temperature of 170°F. and at 
voltage of 4.1. The operation is as follows: 



94 



THE WORKING OF STEEL 



Operation 




No. 


Contents of bath ■ 


Purpose 


1 


Gasolene 


To remove grease 


2 


Sawdust 


To dry 


3 


Warm potassium hydroxide solution 


To remove grease and dirt 


4 


■Warm water 

Warm sulphuric acid solution 


To wash 


5 


To acid clean 


6 


Warm water 


To wash 


7 


Cold water 


Additional wash 


8 


Cold potassium cyanide solution 


Cleanser 


9 


Cold water 


To wash 


10 


Electric cleaner, warm sodium hy- 


Cleanser to give good 




droxide case-iron anode 


plating surface 


11 


Copper plating both of copper sul- 
phate and potassium cyanide solu- 
tion warm 


Plating bath 



There are also other methods of preventing case-hardening, 
one being to paint the surface with a special compound prepared 
for this purpose. In some cases a coating of plastic asbestos is 
used while in others thin sheet asbestos is wired around the part 
to be kept soft. 



PREPARING PARTS FOR LOCAL CASE-HARDENING 

At the works of the Dayton Engineering Laboratories Com- 
pany, Dayton, Ohio, they have a large quantity of small shafts, 



Ve.-0.84"--- 




040SL 

o.40 fr- 



2.332" 
"2.333'- r ~ 



-H 



O.I77"-0.)78" Ream 
must not be over 
am" of f ' 



0.4985" 
Grind 0.4990" 



T — T 
A 



cf< 






$^0,375" Max. 

h - 3.257"—- — 

Fig. 38. — Shaft to be coated with paraffin 



Turn this End' 
after Carbonizing I 

----- — >l 



Fig. 38, that are to be case-hardened at A while the ends B and C 
are to be left soft. Formerly, the part A was brush-coated with 
melted paraffin but, as there were many shafts, this was tedious 
and great care was necessary to avoid getting paraffin where it was 
not wanted. 

To insure uniform coating the device shown in Fig. 39 was 
made. Melted paraffin is poured in the well A and kept liquid 
by setting the device on a hot plate, the paraffin being kept high 



CASE-HARDENING OR SURF AC E-CARBURI ZING 



95 



enough to touch the bottoms of the rollers. The shaft to be 
coated is laid between the rollers with one end against the gage 
B, when a turn or two of the crank C will cause it to be evenly- 
coated. 




Fig. 39. — Device for coating the shaft. 



THE PENETRATION OF CARBON 



Carburized mild steel is used to a great extent in the manu- 
facture of automobile and other parts which are likely to be 
subjected to rough usage. The strength and ability to withstand 
hard knocks depend to a very considerable degree on the thorough- 
ness with which the carburizing process is conducted. 

Many automobile manufacturers have at one time or another 
passed through a period of unfortunate breakages, or have found 
that for a certain period the parts turned out of their hardening 
shops were not sufficiently hard to enable the rubbing surfaces 
to stand up against the pressure to which they were subjected. 



96 THE WORKING OF STEEL 

So many factors govern the success of hardening that often 
this succession of bad work has been actually overcome without 
those interested realizing what was the weak point in their 
system of treatment. As the question is one that can create a 
bad reputation for the product of any firm it is well to study the 
influential factors minutely. 

INTRODUCTION OF CARBON 

The matter to which these notes are primarily directed is the 
introduction of carbon into the case of the article to be hardened. 
In the first place the chances of success are increased by selecting 
as few brands of steel as practicable to cover the requirements 
of each component of the mechanism. The hardener is then able 
to become accustomed to the characteristics of that particular 
material, and after determining the most suitable treatment for 
it no further experimenting beyond the usual check-test pieces 
is necessary. 

Although a certain make of material may vary in composition 
from time to time the products of a manufacturer of good steel 
can be generally relied upon, and it is better to deal directly with 
him than with others. 

In most cases the case-hardening steels can be chosen from the 
following: (1) Case-hardening mild steel of 0.10 per cent caibon; 
(2) case-hardening mild steel of 0.15 per cent carbon; (3) case- 
hardening nickel steel of 2 per cent nickel; (4) case-hardening 
nickel steel of 5 per cent nickel. After having chosen a suitable 
steel it is best to have the sample analyzed by three metallurgists 
and also to have test pieces machined and pulled. 

To prepare samples for analysis place a sheet of paper on the 
table of a drilling machine, and with a %-m. diameter drill, 
machine a few holes about %-m. deep in various parts of the 
sample bar, collecting about 3 oz. of fine drillings free from dust. 
This can be placed in a bottle and dispatched to the metallurgist 
with instructions to search for carbon, silicon, manganese, 
sulphur, phosphorus and nickel. The results of the different 
tests should be carefully tabulated, and as there would most 
probably be some variation an average should be made as a fair 
basis of each element present, and the following tables may be 
used with confidence when deciding if the material is reliable 
enough to be used: 



CASE-HARDENING OR SVRFACE-CARBURIZING 97 

Table 16. — Case-hardening Mild Steel of 0.10 Per Cent Carbon 

Carbon . 08 to . 14 per cent 

Silicon Not over . 20 per cent 

Manganese Not over . 06 per cent 

Sulphur Not over . 04 per cent 

Phosphorus Not over . 04 per cent 

A pull on a test bar ground to V4 sq. in. in area should register at least 

6 tons, being equal to 24 tons per square inch. 

Table 17. — Case-hardening Mild Steel of 0.15 Per Cent Carbon 

Carbon . 12 to . 20 per cent 

Silicon Not over . 20 per cent 

Manganese . 65 to 1 per cent 

Sulphur Not over . 07 per cent 

Phosphorus Not over . 07 per cent 

Tensile breaking strength should be 25 to 33 tons per square inch. 

Table 18. — Case-hardening Nickel Steel of 2 Per Cent Nickel 

Carbon 0.10 to 0.15 per cent 

Silicon Not over . 30 per cent 

Manganese . 25 to . 50 per cent 

Sulphur Not over . 05 per cent 

Phosphorus Not over . 05 per cent 

Nickel 2 to 2 . 50 per cent 

Tensile breaking strength 25 to 35 tons per square inch. 

Table 19. — Case-hardening Nickel Steel of 5 Per Cent Nickei 

Carbon Not over . 15 per cent 

Silicon Not over . 20 per cent 

Manganese Not over . 04 per cent 

Sulphur Not over . 05 per cent 

Phosphorus Not over 0. 05 per cent 

Nickel 4 . 75 to 5 . 75 per cent 

Tensile breaking strength 25 to 40 tons per square inch. 

Having determined what is required we now proceed to inquire 
into the question of carburizing, which is of vital importance. 

USING ILLUMINATING GAS 

The choice of a carburizing furnace depends greatly on the 
facilities available in the locality where the shop is situated and 
the nature and quantity of the work to be done. The furnaces 
can be heated with producer gas in most cases, but when space 
is of value illuminating gas from a separate source of supply has 
some compensations. When the latter is used it is well to install 
a governor if the pressure is likely to fluctuate, particularly where 
the shop is at a high altitude or at a distance from the gas supply. 

Many furnaces are coke-fired, and although greater care is 

7 



98 THE WORKING OF STEEL 

required in maintaining a uniform temperature good results 
have been obtained. The use of electricity as a means of reaching 
the requisite temperature is receiving some attention, and no 
doubt it would make the control of temperature comparatively 
simple. However, the cost when applied to large quantities of 
work will, for the present at least, prevent this method from 
becoming popular. It is believed that the results obtainable 
with the electric furnace would surpass any others; but the 
apparatus seems apt to burn out quickly; besides the necessity 
for frequent rewiring makes it impracticable at present. 

The most elementary medium of carburization is pure carbon, 
but the rate of carburization induced by this material is very low, 
and other components are necessary to accelerate the process. 
Many mixtures have been marketed, each possessing its indi- 
vidual merits, and as the prices vary considerably it is difficult 
to decide which is the most advantageous. 

Absorption from actual contact with solid carbon is decidedly 
slow, and it is necessary to employ a compound from which 
gases are liberated, and the steel will absorb the carbon from the 
gases much more readily. 

Both bone and leather charcoal are more readily volatilized 
than wood charcoal, and although the high sulphur content of the 
leather is objectionable as being injurious to the steel, as also is 
the high phosphorus content of the bone charcoal, they are both 
preferable to the wood charcoal. 

By mixing bone charcoal with barium carbonate in the pro- 
portions of 60 per cent of the former to 40 per cent of the latter 
a very reliable compound is obtained. 

The temperature to which this compound is subjected causes 
the liberation of barium monoxide by contact with the charcoal 
with which it is surrounded. 

Many more elaborate explanations may be given of the actions 
and reactions taking place, but the above is a satisfactorjr guide 
to indicate that it is not the actual compound which causes 
carburization, but the gases released from the compound. 

Until the temperature of the muffle reaches about 300°C. 
carburization does not take place to any useful extent, and conse- 
quently it is advisable to avoid the use of any compound from 
which the carburizing gases are liberated much before that 
temperature is reached. In the case of steel containing nickel 
slightly higher temperatures may be used and are really necessary 



CASE-HARDENING OR SURFACE-CARBURIZING 



99 



if the same rate of carbon penetration is to be obtained, as the 
presence of nickel resists the penetration. 

At higher temperatures the rate of penetration is higher, but 
not exactly in proportion to the temperature, and the rate is 
also influenced by the nature of the material and the efficiency of 
the compound employed. 

The so-called saturation point of mild steel is reached when 
the case contains 0.90 per cent of carbon, but this amount is 
frequently exceeded. Should it be required to ascertain the 
amount of carbon in a sample at varying depths below the skin 



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Degrees of Hardness 
Fig. 40. — Chart showing penetration of carbon. 

this can be done by turning off a small amount after carburizing 
and analyzing the turnings. This can be repeated several times, 
and it will probably be found that the proportion of carbon 
decreases as the test piece is reduced in diameter unless decar- 
burization has taken place. 

The chart, Fig. 40, is also a good guide. 

In order to use the chart it is necessary to harden the sample 
we desire to test as we would harden a piece of tool steel, and then 
test by scleroscope. By locating on the chart the point on the 
horizontal axis which represents the hardness of the sample the 
curve enables one to determine the approximate amount of 
carbon present in the case. 



100 THE WORKING OF STEEL 

Should the hardness lack uniformity the soft places can be 
identified by etching. To accomplish this the sample should 
be polished after quenching and then washed with a weak 
solution of nitric acid in alcohol, whereupon the harder points 
will show up darker than the softer areas. 

The selection of suitable boxes for carburizing is worthy of a 
little consideration, and there can be no doubt that in certain 
cases results are spoiled and considerable expense caused by 
using unsuitable containers. 

As far as initial expense goes cast-iron boxes are probably the 
most expedient, but although they will withstand the necessary 
temperatures they are liable to split and crack, and when they 
get out of shape there is much difficulty in straightening them. 

The most suitable material in most cases is steel boiler plate 
% or 3^ in. thick, which can be made with welded joints and 
will last well. 

The sizes of the boxes employed depend to a great extent on 
the nature of the work being done, but care should be exercised 
to avoid putting too much in one box, as smaller ones permit the 
heat to penetrate more quickly, and one test piece is sufficient to 
give a good indication of what has taken place. If it should be 
necessary to use larger boxes it is advisable to put in three or 
four test pieces in different positions to ascertain if the penetration 
of carbon has been satisfactory in all parts of the box, as it is 
quite possible that the temperature of the muffle is not the same 
at all points, and a record shown by one test piece would not 
then be applicable to all the parts contained in the box. It has 
been found that the rate of carbon penetration increases with 
the gas pressure around the articles being carburized, and it is 
therefore necessary to be careful in sealing up the boxes after 
packing. When the articles are placed within and each entirely 
surrounded by compound so that the compound reaches to 
within 1 in. of the top of the box a layer of clay should be run 
around the inside of the box on top of the compound. The lid, 
which should be a good fit in the box, is then to be pressed on top 
of this, and another layer of clay run just below the rim of the 
box on top of the cover. 

A SATISFACTORY LUTING MIXTURE 

A mixture of fireclay and sand will be found very satisfactory 
for closing up the boxes, and by observing the appearance of the 



CASE-HARDENING OR SURFACE-CARBURIZING 101 

work when taken out we can gage the suitability of the methods 
employed, for unless the boxes are carefully sealed the work is 
generally covered with dark scales, while if properly done the 
articles will be of a light gray. 

By observing the above recommendations reliable results can 
be obtained, and we can expect uniform results after quenching. 

GAS CONSUMPTION FOR CARBURIZING 

Although the advantages offered by the gas-fired furnace for 
carburizing have been generally recognized in the past from points 
of view as close temperature regulation, decreased attendance, 
and greater convenience, very little information has been pub- 
lished regarding the consumption of gas for this process. It has 
therefore been a matter of great difficulty to obtain authentic 
information upon this point, either from makers or users of such 
furnaces. 

In view of this, the details of actual consumption of gas on a 
regular customer's order job will be of interest. The "Revergen" 
furnace, manufactured by the Davis Furnace Company, Luton, 
Bedford, England, was used on this job, and is provided with 
regenerators and fired with illuminating gas at ordinary pressure, 
the air being introduced to the furnace at a slight pressure of 
3 to 4 in. water gage. The material was charged into a cold 
furnace, raised to 1,652°F., and maintained at that temperature 
for 8 hr. to give the necessary depth of case. The work consisted 
of automobile gears packed in six boxes, the total weight being 
713 lb. The required temperature of 1,652°F. was obtained in 70 
min. from lighting up, and a summary of the data is shown in 
the following table : 



Gas to raise furnace and charge from cold to 

1,652°F., 70 min 

Gas to maintain 1,652°F. for 1st hour 

Gas to maintain 1,652°F. for 2nd hour 

Gas to maintain 1,652°F. for 3rd hour 

Gas to maintain 1,652°F. for 4th hour 

Gas to maintain 1,652°F. for 5th hour 

Gas to maintain 1,652°F. for 6th hour 

Gas to maintain 1,652°F. for 7th hour 

Gas to maintain 1,652°F. for 8th hour 



Cubic Foot 

Per Pound 

of Load 


Total 
Number of 
Cubic Foot 


1.29 


925 


0.38 


275 


0.42 


300 


0.38 


275 


0.42 


300 


0.49 


350 


0.49 


350 


0.45 


325 


0.45 


325 



102 THE WORKING OF STEEL 

The overall gas consumption for this run of 9 hr. 10 min. was 
only 4.8 cu. ft. per pound of load. 

THE CARE OF CARBURIZ1NG COMPOUNDS 

Of all the opportunities for practicing economy in the heat- 
treatment department, there is none that offers greater possi- 
bilities for profitable returns than the systematic cleaning, blend- 
ing and reworking of artificial carburizers, or compounds. 

The question of whether or not it is practical to take up the 
work depends upon the nature of the output. If the sole product 
of the hardening department consists of a 1.10 carbon case or 
harder, requiring a strong highly energized material of deep 
penetrative power such as that used in the carburizing of ball 
races, hub-bearings and the like, it would be best to dispose of the 
used material to some concern whose product requires a case with 
from 0.70 to 0.90 carbon, but where there is a large variety of 
work the compound may be so handled that there will be practi- 
cally no waste. 

This is accomplished with one of the most widely known arti- 
ficial carburizers by giving all the compound in the plant three 
distinct classifications: "New," being direct from the maker; 
"half and half," being one part of new and one part first run; and 
"2 to 1," which consists of two parts of old and one part new. 

SEPARATING THE WORK FROM THE COMPOUND 

During the pulling of the heat, the pots are dumped upon a 
cast-iron screen which forms a table or apron for the furnace. 
Directly beneath this table is located one of the steel conveyor 
carts, shown in Fig. 41, which is provided with two wheels at the 
rear and a dolly clevis at the front, which allows it to be hauled 
away from beneath the furnace apron while filled with red- 
hot compound. A steel cover is provided for each box, and the 
material is allowed to cool without losing much of the evolved 
gases which are still being thrown off by the compound. 

As this compound comes from the carburizing pots it contains 
bits of fireclay which represent a part of the luting used for sealing, 
and there may be small parts of work or bits of fused material 
in it as well. After cooling, the compound is very dusty and 



CASE-HARDENING OR SURFACE-CARBURIZING 103 




Fig. 41. — The cooling carts. 




Fig. 42. — Machine for blending the mixture. 



104 THE WORKING OF STEEL 

disagreeable to handle, and, before it can be used again, must be 
sifted, cleaned and blended. 

Some time ago the writer was confronted with this proposition 
for one of the largest consumers of carburizing compound in the 
world, and the problem was handled in the following manner: 
The cooled compound was dumped from the cooling cars and 
sprinkled with a low-grade oil which served the dual purposes of 
settling the dust and adding a certain percentage of valuable 
hydrocarbon to the compound. In Fig. 42 is shown the machine 
that was designed to do the cleaning and blending. 

BLENDING THE COMPOUND 

Essentially, this consists of the sturdy, power-driven separator 
and fanning mill which separates the foreign matter from the 
compound and elevates it into a large settling basin which is 
formed by the top of the steel housing that incloses the apparatus. 
After reaching the settling basin, the compound falls by gravity 
into a power-driven rotary mixing tub which is directly beneath 
the settling basin. Here the blending is done by mixing the 
proper amount of various grades of material together. After 
blending the compound, it is ready to be stored in labeled con- 
tainers and delivered to the packing room. 

It will be seen that by this simple system there is the least 
possible loss of energy from the compound. The saving com- 
mences the moment the cooling cart is covered and preserves the 
valuable dust which is saved by the oiling and the settling basin 
of the blending machine. 

Then, too, there is the added convenience of the packers who 
have a thoroughly cleaned, dustless, and standardized product 
to work with. Of course, this also tends to insure uniformity in 
the case-hardening operation. 

With this outfit, one man cleans and blends as much compound 
in one hour as he formerly did in ten. 



CHAPTER VIII 
HEAT TREATMENT OF STEEL 

Heat treatment is a somewhat vague term. As commonly 
used it may be said to include everything from annealing to 
tempering. The proper use would seem to be confined to such 
heating and quenching as so changes the quality of the steel as 
to make it more suitable for its purpose. 

To properly heat-treat steel we must know its composition and 
at what degrees the critical changes occur. Steels for treatment 
should be classified into two distinct groups. 

In the first group are the alloy steels; those that carry certain 
percentages of manganese, chromium, nickel, vanadium or other 
elements. The purpose of heat treatment for the alloy group is 
to increase strength and toughness of material and at the same 
time to increase machining ability by leaving steel ductile. 

The second group includes the hardening and tempering of 
crucible steels. 

Heat treating includes annealing, case-hardening and the 
relieving of strains from hardening or forging operations. 

From text books we know that iron possesses the allotropic 
property of existing in three different conditions and still remain 
the same chemically. If we heat pure iron to 1,390°F. it 
suddenly loses its magnetism, and instead of being soft and ductile 
it becomes hard and brittle. If we continue to heat it until 
it reaches 1,635°F. it again suddenly changes its properties and 
instead of being brittle becomes again ductile, but still hard and 
non-magnetic. These stages of iron are called, respectively: 

Alpha Iron: Soft and ductile and stable below lower critical point. 

Beta Iron: Hard and brittle, stable between critical points. 

Gamma Iron: Hard and ductile and stable above high critical point. 

Now if carbon is added to the iron, the critical point is lowered 
in direct proportion to percentage of carbon, until point of 
calescense is reached, which in high-carbon steels is about 1,350°F 

Composition of Steel. — The composition of steel is given by 
Professor Sauveur, as follows: 

105 



106 THE WORKING OF STEEL 

First. — Ferrite, which is pure iron, low in tensile strength, but very soft 
and ductile. 

Second. — Cementite, which is a carbide of iron, present in steel over 0.90 
carbon, very hard and brittle. 

Third. — Pearlite, which is simply a mechanical mixture of pure iron with 
cementite. 

Pearlite is present in steel in increasing percentage up to 0.90 
carbon, with a corresponding decrease of ferrite. At 0.90 carbon 
the steel is all pearlite. When carbon is over 0.90 the pearlite 
decreases in percentage with a corresponding increase of per- 
centage of cementite. 

Every condition of heat on steels, from low critical point to 
that above high critical or overheated steel, has been recorded by 
numerous authors on the subject. 

DIFFERENT STEEL STRUCTURES 

We will touch on them briefly, not because of any actual value 
to the operator, but simply to show that a difference of a few 
degrees in heating gives a different structure of steel, easily 
recognizable under a microphotograph. 

Osmondite appears at about 750°F. when cementite begins to 
dissolve in Alpha iron. 

Sorbite appears at 1,100°F. and is nearly all pearlite but with a 
certain percentage of cementite undissolved. 

Pearlite is thoroughly saturated Alpha iron with cementite. 

Troostite is the higher carbon steels in tempered conditions. 

Martensite is properly hardened steel. 

Austentite is present in high-carbon overheated steel. 

Now to determine the transformations in both hardening and 
tempering alloy steel, the question will naturally arise as to the 
need of first hardening such steels and then tempering until it 
becomes ductile. 

The reason is that as steel solidifies after pouring it cools very 
rapidly from liquid state, thereby causing segregation (ferrite 
and cementite do not have time to combine), strains, etc. In 
reheating we bring it beyond the upper critical point to Gamma 
iron, that state wherein the condition is stable. Quenched from 
this temperature the molecules remain in the right crystallic 
form so that a slow tempering process can finish the work and 
deliver a perfect sorbitic or pearlitic saturation, as we may desire. 



HEAT TREATMENT OF STEEL 107 

The Controlling Factors. — The factors which determine treat- 
ment are: 

Carbon is the controlling factor as to determining the critical 
point. In other words, the hardening temperature is determined 
by carbon contents. 

Manganese of 1 per cent or more controls the time of soaking 
at high critical point. 

High silicon will shorten time of soaking somewhat, but low 
silicon will not increase it. 

Chromium of more than 5 points will add 1°F. for each point 
of chromium to hardening heat as predetermined by carbon. For 
instance, if predetermined heat is 1,500°F. and steel to be 
hardened contains 1 per cent or 100 points chromium, add 100°F., 
making critical point 1,600°. 

Nickel of more than 10 points will add approximately one 
minute to soaking time for each point present up to 50 points; 
over 50 points both hardening and tempering heats will change. 

For tempering, a different process is carried out for determina- 
tion of factors. 

Carbon is practically eliminated as no martensite condition 
exists at heat of 700°F. and over. 

Manganese has done its real work keeping a sort of fibrous 
grip on the molecules in suspense. 

Silicon, in conjunction with sulphur and phosphorus, acts as 
lubricants and facilitates the relocation of saturated mass, from 
rigidity to one of ease. Too much of these elements will prevent 
the proper binding of molecules together and weakens structure, 
but all three are a great help for machining operations. Silicon 
should not exceed 0.30, sulphur not over 0.07, and phosphorus not 
over 0.09 per cent. 

Chrome and nickel when present control both temperature and 
time, in direct proportion to its percentage. When chromium is 
present at 1 per cent or more and nickel at 3 per cent or more, 
singly or combined, it becomes a problem not yet solved, to treat 
with any certainty of uniformity as far as ease of machining 
operations are concerned. 

THE DIFFERENT ELEMENTS 

The different elements in ordinary alloy steels have the follow- 
ing functions : 



108 THE WORKING OF STEEL 

Carbon, for hardness and rigidity. 

Manganese, for toughness. 

Silicon, a sort of adjuster. 

Sulphur and phosphorus, as lubricants. 

Chromium, as a refiner of grain and to add hardness to help carbon. 

Nickel, as a protecting support of structure and aid to stability. 

Vanadium, in small doses, acts as a scavenger, in high percentage it helps 
to resist friction. 

Tungsten, to add keen cutting qualities and when present in sufficient 
quantity to resist heat. 

In the heat treating of alloy steel you have certain factors to 
bear in mind. These factors may vary slightly as to duration of 
heat and time limits, but they are always present. 

First. — You must know critical points. 

Second. — You must not fall below high critical point when soaking steel. 

Third. — Steel of same analysis must be subjected to same heat and same 
length of time for soaking to give uniform results. 

Fourth. — Quenching must be done in both within certain limits of tem- 
perature, depending on quality of work performed. 

Fifth. — Tempering heats range on 10°F. basis. Heat must be established 
on quality of work desired. 

Sixth. — A low limit must be set as to time necessary for soaking at high 
heat. This heat must not fall below that wanted, while being soaked, or 
time must again begin when temperature is again reached. Too long soak- 
ing may cause a reaction, giving a dry steel, with a great drop in elastic 
strength. 

Seventh. — -When work is taken out of furnace for tempering or annealing 
purposes it must be thoroughly covered. No chance must be left to form 
air pockets. Air-cooled steel will often contain hard spots on surface and 
soft spots in interior. 

THE CRITICAL POINTS 

The point of calescence can be determined by pyrometer, by 
closely watching the needle. A thermo-couple or fire end should 
be inserted in the steel. Drill a hole in a piece of steel to take in 
end of thermo-couple. As the heat advances, the needle will 
follow until it reaches a point where it suddenly stops, wavers and 
then suddenly drops several degrees although heat is constantly 
advancing. Then the needle will again suddenly commence its 
upward swing. Where the needle stops and rests, is calescence or 
low critical point. 

Now reverse the operation. Heat beyond the critical point, 
shut off the fuel, and watch for the same phenomena. The needle 
will start to drop back, then suddenly stop and advance several 



HEAT TREATMENT OF STEEL 



109 



degrees, after which it again starts to drop and continues down the 
scale. This upper change is called the recalescence point. 

The Magnet Test. — The critical point can also be determined by 
an ordinary horse shoe magnet. Touch the steel with a magnet 
during the heating and when it reaches the temperature at which 
steel fails to attract the magnet, or in other words, loses its 




Fig. 43. — Finding hardening heats with a magnet. 

magnetism, the point of calescence or critical point has been 
reached. 

Figures 43 and 44 show how these are used in practice. 

The first (Fig. 43) shows the use of a permanent horse shoe 
magnet and the second (Fig. 44) an electro-magnet consisting 
of an iron rod with a coil or spool magnet at the outer end. In 
either case the magnet should not be allowed to become heated 
but should be applied quickly. 




Fig. 44. — Using electro-magnet to determine heat. 



The work is heated up slowly in the furnace and the magnet 
applied from time to time. The steel being heated will attract 
the magnet until the heat reaches the critical point. The mag- 
net is applied frequently and when the magnet is no longer 
attracted, the piece is at the lowest temperature at which it 
can be hardened properly. Quenching at this point will give a tool 
of satisfactory hardness. 



110 THE WORKING OF STEEL 

JUDGING THE HEAT OF STEEL 

While the use of a pyrometer is of course the only way to 
have accurate knowledge as to the heat being used in either 
forging or hardening steels, a color chart will be of considerable 
assistance if carefully studied. These have been prepared by 
several of the steel companies as a guide, but it must be remem- 
bered that the colors and temperatures given are only approximate, 
and can be nothing else. 

Different kinds of steel should be heated to different tem- 
peratures. High-speed steel, for example, can be heated to a 
white heat, or about 2,200°F. which is No. 11 on the scale given. 
But when made up into twist drills, milling cutters and similar 
tools it should only be heated up to No. 10. 

With carbon steels a much lower temperature is necessary. 
They should not be heated above a bright red for forging, this 
being perhaps 1,650°F. and for hardening the temperature should 
not exceed 1,500°F. In general the hardening temperature 
lies between 1,400° and 1,500°F. 

It is extremely difficult to give very definite instructions, as 
experience with the particular kind of steel you are using is the 
only way to be sure of your results. It is well to remember, 
however, that the lowest heat at which the piece, will harden 
satisfactorily is the best heat for that piece and that it is always 
safer to have the heat a trifle too low than too high. Milling 
cutters or other tools which are light and fragile, or have many 
cuts in them, do not require as much heat for hardening as do 
solid pieces of the same kind and size. 

Always reheat steel after forging, do not try to temper at the 
same heat. It is also important to have the heating for 
hardening as uniform as possible. 

Overheating does not increase the hardness but it does make 
the steel more brittle. It is safer to take a chance with a low 
heat as in that case you can reharden, while with an overheat the 
piece is very likely to be spoiled. 

Always use enough hardening liquid to prevent its becoming 
too warm before the piece cools, but do not have it too cold 
when the piece is dipped into it. If water is used it should be 
pure and have a temperature of about 60°F. A leeway of 
5° either way will do no harm. 

For tempering with oil use a fish oil or linseed oil instead of 



HEAT TREATMENT OF STEEL 111 

fatty oils. Always keep the tool in motion in the hardening 
bath until it becomes fairly cool. Also avoid sharp limits 
between the hardened and unhardened portions. In the case 
of a lathe tool move the tool in and out of the liquid as well as 
with a circular bath. Otherwise cracks are very apt to develop 
at the point where the tool has left the hardening liquid. 

Tempering, or drawing the temper, relieves some of the stresses 
imposed by the sudden cooling of the piece and increases the 
elasticity, or ability to withstand shocks because it reduces its 
brittleness. It is always safer to select a steel which is harder 
than may be necessary and draw the temper lower than to 
select a softer steel and leave the temper harder. The first 
piece will be hard enough and much stronger while the second 
will be brittle and not satisfactory. 

HEAT TREATMENT OF GEAR BLANKS 

This section is based on a paper read before the American 
Gear Manufacturers' Association at White Sulphur Springs. 
W. Va., Apr. 18, 1918, and outlines the advantages of thoroughly 
annealed blanks to the subsequent machining and hardening 
operations, as well as an exposition of the structural changes 
undergone by a piece of steel in the heat-treating process. 

Great advancement has been made in the heat treating and 
hardening of gears. In this advancement the chemical and 
metallurgical laboratory have played no small part. During 
this time, however, the condition of the blanks as they come to 
the machine shop to be machined has not received its share of 
attention in the heat-treating department of many forge shops, 
and in many cases has been neglected or not considered by the 
machine shops themselves. This is especially true of shops using 
only the lower carbon steels. 

There are two distinct types of gears, both types having their 
champions, namely, carburized and heat-treated. The difference 
between the two in the matter of steel composition is entirely 
in the carbon content, the carbon never running higher than 
25-point in the carburizing type, while in the heat-treated gears 
the carbon is seldom lower than 35-point. The difference in the 
final gear is the hardness. The carburized gear is file hard on the 
surface, with a soft, tough and ductile core to withstand shock, 
while the heat-treated gear has a surface that can be touched by 
a file with a core of the same hardness as the outer surface. 



112 THE WORKING OF STEEL 

Annealing Work. — With the exception of several of the higher 
types of alloy steels, where the percentages of special elements 
run quite high, which causes a slight air-hardening action, the 
carburizing steels are soft enough for machining when air cooled 
from any temperature, including the finishing temperature at 
the hammer. This condition has led many drop-forge and manu- 
facturing concerns to consider annealing as an unnecessary opera- 
tion and expense. In many cases the drop forging has only 
been heated to a low temperature, often just until the piece 
showed color, to relieve the so-called hammer strains. While 
this has been only a compromise it has been better than no re- 
heating at all, although it has not properly refined the grain, 
which is necessary for good machining conditions. 

Before going into the effects of proper annealing temperatures 
for the most commonly used steels we will briefly consider the 
theory of heat treatment. Heat treatment, in the broad sense, is 
the thermal refinement of the structure of steel, and covers the 
four operations, namely, annealing, carburizing, hardening and 
drawing, or tempering as it is commonly called. All of these 
operations are based on the fact that in heating a piece of steel 
the structure undergoes a change at from one to three points on 
heating and a corresponding number of changes on cooling, these 
changes being caused by a molecular rearrangement of the carbon 
and iron. The points are known as "critical points" or "critical 
ranges" and vary in number according to the composition of the 
steel. These points on heating are often referred to as "decal- 
escent point," and on cooling as "recalescent point." 

Carbon exerts the greatest influence on the location of the 
critical points, with nickel and chromium coming next. A 
straight-carbon steel up to 35-point carbon has three critical 
points; from 35- to 89-point carbon two critical points are found 
and over 89-point carbon only one critical temperature is found. 
Each 1 per cent of nickel will lower the critical point 20°F., while 
each 1 per cent of chromium raises the point 10°F. Of the critical 
points those found on a rising temperature are higher than the 
corresponding points on a falling temperature. Rising tempera- 
tures are always considered in correctly heat treating a piece of 
steel. In order to produce the most complete rearrangement of 
the molecules of carbon and iron and therefore the greatest re- 
finement it is necessary to heat to a temperature slightly in excess 
of the highest critical point. 



HE A T TREA TMENT OF STEEL 113 

Annealing is heating to a temperature slightly above the high- 
est critical point and cooling slowly either in the air or in the 
furnace. Annealing is done to accomplish two purposes: (1) 
to relieve mechanical strains and (2) to soften and produce a 
maximum refinement of grain. 

Process of Carburizing. — Carburizing imparts a shell of high- 
carbon content to a low-carbon steel. This produces what might 
be termed a "dual" steel, allowing for an outer shell which when 
hardened would withstand wear, and a soft ductile core to pro- 
duce ductility and withstand shock. The operation is carried 
out by packing the work to be carburized in boxes with a material 
rich in carbon and maintaining the box so charged at a tempera- 
ture in excess of the highest critical point for a length of time to 
produce the desired depth of carburized zone. Generally main- 
taining the temperature at 1,650 to 1,700°F. for 7 hi*, will pro- 
duce a carburized zone }^2 m - deep. 

Heating to a temperature slightly above the highest critical 
point and cooling suddenly in some quenching medium, such as 
water or oil hardens the steel. This treatment produces a maxi- 
mum refinement with the maximum strength. 

Drawing to a temperature below the highest critical point 
(the temperature being governed by the results required) relieves 
the hardening strains set up by quenching, as well as the reducing 
of the hardness and brittleness of hardened steel. 

As the maximum refinement of the grain size of a piece of steel 
takes place at a temperature at or slightly above the highest 
critical point, increasing temperatures over that point correspond- 
ingly increases the grain size. The grain size of a piece of steel 
is governed by the maximum temperature reached after passing- 
over the highest critical point or by the temperature at which 
the last mechanical working was given the steel, providing the 
mechanical work was done at a temperature in excess of the 
highest critical point. 

Annealed steels are called pearlitic, "pearlite" being the name 
applied to the microstructure of slowly cooled steels. Pearlite is 
a mechanical mixture consisting of alternate masses in ferrite (pure 
iron) and cementite (cementite being a compound made up of 6.6 
per cent carbon and 93.4 per cent ferrite) with the resultant 
mixture containing 0.89 per cent carbon. Pearlite may be pres- 
ent in two forms, lamellar and granular, with the granular occur- 
ring either coarse or fine or elongated with bands of ferrite 
separating the elongated grains of pearlite. 



114 THE WORKING OF STEEL 

When etched in a weak alcoholic solution of picric or nitric 
acid and examined under the microscope the ferrite, untouched 
by the etching solution, appears white, while the pearlite shows 
up black. 

Effect of Proper Annealing. — Proper annealing of low-carbon 
steels causes a complete solution or combination to take place 
between the ferrite and pearlite, producing a homogeneous mass 
of small grains of each, the grains of the pearlite being surrounded 
by grains of ferrite. A steel of this refinement will machine to 
good advantage, due to the fact that the cutting tool will at all 
times be in contact with metal of uniform composition and will 
not be alternately coming in contact with the soft ferrite con- 
stituent and the harder carbon particles. 

While the alternate bands of ferrite and pearlite are micro- 
scopically sized, it has been found that with a Gleason or Fellows 
gear-cutting machine that rough cutting can be traced to poorly 
annealed steels, having either a pronounced banded structure or a 
coarse granular structure. A study of the microphotographs of 
several of the widely used low-carbon steels in gear manufacture 
will show the condition of the structure direct from the drop 
hammer, the pronounced banded structure of ferrite and pearlite 
and the change produced by thorough annealing. 

Temperature for Annealing. — Theoretically, annealing should 
be accomplished at a temperature at just slightly above the critical 
point. However, in practice the temperature is raised to a 
higher point in order to allow for the solution of the carbon and 
iron to be produced more rapidly, as the time required to produce 
complete solution is reduced as the temperature increases past 
the critical point. Temperatures exceeding the critical point by 
over 100°F. should never be used on account of the enlargement 
of the grains of pearlite and ferrite. Microphotographs of a 
piece of steel annealed at temperatures increasing by 25°F. from 
a point below the critical point to the burning point show clearly 
the effects of temperature on the grain size. 

For annealing the simpler types of low-carbon steels the follow- 
ing temperatures have been found to produce uniform machining 
conditions on account of producing uniform fine-grain pearlite 
structure : 

1.15 to 0.25 Per Cent Carbon, Straight Carbon Steel. — Heat 
to 1,650°F. Hold at this temperature until the work is uniform- 
ly heated; pull from the furnace and cool in air. 



HEAT TREATMENT OF STEEL 115 

0.15 to 0.25 Per Cent Carbon, \y 2 Per Cent Nickel, Y 2 Per 
Cent Chromium Steel. — Heat to 1,600°F. Hold at this tempera- 
ture until the work is uniformly heated; pull from the furnace 
and cool in air. 

0.15 to 0.25 Per Cent Carbon, 3% Per Cent Nickel Steel- 
Heat to 1,575°F. Hold at this temperature until the work is 
uniformly heated; pull from the furnace and cool in air. 

In the annealing of the higher types of chrome-nickel steel, 
with the nickel content running about 3 per cent and the chro- 
mium about 1 per cent the operation is more difficult, as rapid 
cooling through the upper critical range produces a hardness due 
to the slight air-hardening properties of steel of this composition. 
The annealing of this type of steel requires considerably more 
attention both in the heating and cooling. To produce the best 
machinability of this steel the following practice will give very 
satisfactory results : 

Heat to a temperature about 100°F., in excess of the critical 
point, holding at this temperature for a considerable time to allow 
for thorough heating and complete solution of the cementite; cool 
rapidly, either by pulling from the furnace into air or opening up 
the furnace doors to a point at which the forgings show no color 
in daylight; reheat to a point just in excess of the highest critical 
point and cool slowly in the furnace. The temperatures, length 
of heating, and time and rate of cooling are dependent on analysis, 
size of forging and weight of the load of forgings in the furnace. 

Care in Annealing. — Not only will benefits in machining be 
found by careful annealing of forgings but the subsequent troubles 
in the hardening plant will be greatly reduced. The advantages 
in the hardening start with the carburizing operation, as a steel 
of uniform and fine grain size will carburize more uniformly, pro- 
ducing a more even hardness and less chances for soft spots. The 
holes in the gears will also " close in more uniformly," not caus- 
ing some gears to require excessive grinding and others with just 
enough stock. Also all strains will have been removed from the 
forging, eliminating to a great extent distortion and the noisy 
gears which are the result. 

With the steels used for the heat-treated gears, always of a 
higher carbon content, treatment after forging is necessary for 
machining, as it would be impossible to get the required produc- 
tion from untreated forgings, especially in the alloy steels. The 
treatment is more delicate, due to the higher percentage of carbon 



116 THE WORKING OF STEEL 

and the natural increase in cementite together with complex 
carbides which are present in some of the higher types of alloys. 
Due to the many analyses of heat-treated gear steer it is impos- 
sible to give in this paper specific treatments. 

More time should be given to permit complete solution to 
take place and the rate of cooling watched closely, together with 
the temperature at which the forgings are pulled from the fur- 
nace. For a furnace load weighing 550 lb. of medium-section 
steel forgings 0.50 per cent carbon, 0.60 per cent manganese, 3 per 
cent nickel, 1 per cent chromium the following treatment gave 
very good machining conditions on turning operations as well as 
on the Fellows gear-shaping machine: 

Heat to 1,330°F., taking 2 hr.to heat to the temperature. Hold 
at the temperature for 1% hr. and allow to cool in furnace to 
1,170°F., taking about 1 hr. to cool. Reheat to 1,230°F., 
consuming % hr. to reheat. Hold at 1,230°F. for 134 hr. Cool 
slowly in furnace, not faster than 75° for the first hour, until 
900°F., then cool in air. 

Where poor machining conditions in heat-treated steels are 
present they are generally due to incomplete solution of cementite 
rather than bands of free ferrite, as in the case of case-hardening 
steels. This segregation of carbon, as it is sometimes referred 
to, causes hard spots which, in the forming of the tooth, cause the 
cutter to ride over the hard metal, producing high spots on the 
face of the tooth, which are as detrimental to satisfactory gear 
cutting as the drops or low spots produced on the face of the 
teeth when the pearlite is coarse-grained or in a banded condition. 

In the simpler carburized steels it is not necessary to test the 
forgings for hardness after annealing, but with the high percent- 
ages of alloys in the carburizing steels and the heat-treated steels 
a hardness test is essential. For this test the Brinell hardness 
tester is far more accurate than the sclerescope test. However 
the Brinell test should not be used without the aid of the 
microscope. 

To obtain the best results in machining, the microstructure 
of the metal should be determined and a hardness range set 
that covers the variations in structure that produce good machin- 
ing results. By careful control of the heat-treating operation 
and with the aid of the Brinell hardness tester and the microscope 
it is possible to continually give forgings that will machine 
uniformly and be soft enough to give desired production. The 



HEAT TREATMENT OF STEEL 



117 



following gives a few of the hardness numerals on steel used in 
gear manufacture that produce good machining qualities: 

20 per cent carbon, 3 per cent nickel, 134 per cent chromium — 
Brinell 156-170. 

50 per cent carbon, 3 per cent nickel, 1 per cent chromium — 
Brinell 179-187. 

50 per cent carbon chrome vanadium — Brinell 170-9. 

THE INFLUENCE OF SIZE 
The size of the piece influences the physical properties ob- 
tained in steel by heat treatment. This has been worked out by 
E. J. Jaintzky, metallurgical engineer of the Illinois Steel 
Company, as follows: 



_ 28 



o 24 



fc 20 



V 16 











































































l\ 


















\\\ 




























































































■C^f 





























1 2 3 4 5 6 7 8 

Diameter in Inches 

Fig. 45. — Effect of size on heating. 

"With an increase in the mass of steel there is a corresponding de- 
crease in both the minimum surface hardness and depth hardness, 
when quenched from the same temperature, under identical conditions 
of the quenching medium. In other words, the physical properties 
obtained are a function of the surface of the metal quenched for a given 



118 



THE WORKING OF STEEL 



mass of steel. Keeping this primary assumption in mind, it is possible 
to predict what physical properties may be developed in heat treating 
by calculating the surface per unit mass for different shapes and sizes. 
It may be pointed out that the figures and chart that follow are not 
results of actual tests, but are derived by calculation. They indicate 
the mathematical relation, which, based on the fact that the physical 
properties of steel are determined not alone by the rate which heat is 
lost per unit of surface, but by the rate which heat is lost per unit of 
weight in relation to the surface exposed for that unit. The unit of 
weight has for the different shaped bodies and their sizes a certain sur- 
face which determines their physical properties. 

"For example, the surface corresponding to 1 lb. of steel has been 
computed for spheres, rounds and flats. For the sphere with a unit 
weight of 1 lb. the portion is a cone with the apex at the center of the 
sphere and the base the curved surface of the sphere (surface exposed to 
quenching). For rounds, a unit weight of 1 lb. may be taken as a disk 
or cylinder, the base and top surfaces naturally do not enter into calcu- 
lation. For a flat, a prismatic or cylindrical volume may be taken to 
represent the unit weight. The surfaces that are considered in this 
instance are the top and base of the section, as these surfaces are the 
ones exposed to cooling." 

The results of the calculations are as follows : 



Table 20. — Sphere 

Surface per 

pound of steel 

Y 

2 . 648 sq. in. 

3.531 sq. in. 

5.294 sq. in. 

7 . 062 sq. in. 

2 in 10 . 61 sq. in. 

XY = 21.185. 

Table 21. — Round 



Diameter 

of sphere 

X 

8 in . . . 

6 in . . . 

4 in . . . 

3 in... 



Diameter 
of round 

X 

8.0 

6.0 

5.0 

4.0 

3.0 

2.0 

1.0 

0.5 



Surface per 
pound of steel 
Y 
1 .765 sq. in. 
2.354 sq. in. 
2.829 sq. in. 
3.531 sq. in. 
4.708 sq. in. 



fh 7.062 sq. in. 

in 14 . 125 sq. in. 

in 28 . 25 sq. in. 

0.25 in 56.5 sq. in. 

XY = 14.124. 



HEAT TREATMENT OF STEEL 119 

Table 22.— Flat 

Thickness Surface per 

of flat pound of steel 

X Y 

8.0 in 0.8828 sq. in. 

6.0 in 1.177 sq. in. 

5.0 in 1 . 412 sq. in. 

4.0 in 1.765 sq. in. 

3.0 in....! 2.345 sq. in. 

2.0 in 3 . 531 sq. in. 

1.0 in 7 . 062 sq. in. 

0.5 in 14.124 sq. in. 

0.25 in 28.248 sq. in. 

XY = 7.062. 

Having once determined the physical qualities of a certain speci- 
men, and found its position on the curve we have the means to predict 
the decrease of physical qualities on larger specimens which receive the 
same heat treatment. 

When the surfaces of the unit weight as outlined in the foregoing- 
tables are plotted as ordinates and the corresponding diameters as 
abscissae, the resulting curve is a hyperbola and follows the law XY = 
C. In making these calculations the radii or one-half of the thickness 
need only to be taken into consideration as the heat is conducted from 
the center of the body to the surface, following the shortest path. 

The equations for the different shapes are as follows : 

For flats XY = 7.062 

For rounds XY = 14.124 
For spheres 17 = 21.185 

It will be noted that the constants increase in a ratio of 1, 2, and 3, 
and the three bodies in question will increase in hardness on being 
quenched in the same ratio, it being understood that the diameter of 
the sphere and round and thickness of the flat are equal. 

Relative to shape, it is interesting to note that rounds, squares, 
octagons and other three axial bodies, with two of their axes equal, 
have the same surface for the unit weight. 

For example : 

Size Length Surface Weight Surface for 1 lb. 

2 in. Sq. 12 in. 96.0 sq. in. 13.60 lb. 7.06 sq. in. 

2 in. Round 12 in. 75.4 sq. in. 10.68 lb. 7.06 sq. in. 

Although this discussion is at present based upon mathematical 
analysis, it is hoped that it will open up a new field of investigation in 
which but little work has been done, and may assist in settling the as 
yet unsolved question of the effect of size and shape in the heat treat- 
ment of steel. 



120 THE WORKING OF STEEL 

Heat Treatment of Rifle Parts. — Some idea of the large number 
of parts in a rifle which must be heat-treated may be had from 
the accompanying list. This also gives the practice in both 
hardening and tempering. The information is, of course, equally 
applicable to other parts of a similar nature. 

t, , . f Harden in cyanide at 1,500°F. 

Bayonet catch < _ . . .. 

I Quench in oil. 

Bayonet nut washer and screw. { Blue in niter at 800°F. 

f Case-harden at 780°C, 2Y 2 hr. to 3 hr. 
■o ,, J Quench in oil. 

1 Pack, bone %. 

[ Pack, leather }/i. 

„ ., . f Harden, open fire at 145°F. 

Bolt stop spring. ( Temper ^ niter at ^^ 

B , , ( Case-harden at 750°C., 2}i hr. 

\ Quench in oil. Pack, bone }^, leather }^. 

t, , , . ■ [Harden in open at 1,450°F. 

Butt plate cap spring { ^^ ^ niter at 80()OF 

Butt plate screw, large { Case-harden at 750°C, 2% hr. 

t, . i . ii f Quench in oil. Pack, old bone }■£. Pack, 

Butt plate screw, small < , n , 

I new bone }$. 

( Case-harden at 750°C, 2% hr. 
Cocking piece -j Quench in oil. 

I Pack, whole bone (new). 

r Harden in cyanide at 1,500°F. 
Safety lock plunger \ Quench in oil. 

{ Dip in niter, 1 min. 

r Case harden at 750°C, 2Y 2 hr. 
Sear \ Quench in oil. 

I Pack. Bone %, leather J4- 
s • f Case-harden at 750°C, 2 hr. 
\ Quench in oil. 

C Case harden at 750°C, 23^ hr. 
Sleeve ' \ Quench in oil. 

I Pack in whole bone (new). 
Harden in open at 1,450°F. 



\ Temper in lead at 900°F 

r Case-harden at 750°C, 2\i hr. 

Trigger \ Quench in oil. 

I Pack. Bone %, leather 3^. 

f Case-harden at 750°C, 2%, hr. 

I Pack. Whole bone (new). 

„ -. . . . . ,. f Harden in cyanide at 1,500°F. 

Safety lock spindle \ ~. . ,. , . , , 

I Draw riveting end in lead. 

Guard. { Blue in niter at 800°F. 



HEAT TREATMENT OF STEEL 121 



Guard screw, front and rear 



Lower band spring . 



Case harden at 750 C C, 2)4 hr. 

Quench in oil. 

Pol. head. 

j Blue in niter at 800°F. 

( Pack. Old bone K, new leather J^. 

[Harden in open fire at 1,450°F. 

I Temper in lead at 900°F. 

, , . , f Harden in open fire at 1,450°F. 

Lower band swivel < „ . , , , nrir ,oT7> 

I Temper in lead at 900 F. 

r Harden in open fire at 1,450°F. 
Magazine spring \ Temper in niter at 800°F. 

I Correct over flame. 

r Case-harden at 750°C., 2Y 2 hr. 
Cut-off \ Quench in water. 

I Pack. Bone %, leather Y±. 

„ , „ . „ f Case-harden at 700°C, V/ 2 hr. 

Cut-off spindle < „ ,. 

I Quench in water. 

r Harden in cynide at 1,500°F. 
Cut-*off plunger \ Quench in oil. 

I Dip in niter, 1 min. 

.p. /Harden in cynide at 1,500 C F. 

' ' J Quench in oil. 

„. , f Case-harden at 750°C, 2}4 hr. 

Ejector pm.. • \ Black. 

/ Harden in open fire at 1,450°F. 
Extractor. . . . . ^ Temper in lead &t QQQ o Y 

. . . / Harden in open at 1,450°F. 

\ Temper in lead. 
(• Case-harden at 750°C , 2}i hr. 

Follower \ Quench in oil. 

I Pack. -whole bone (new). 

HEAT-TREATING EQUIPMENT AND METHODS FOR MASS 

PRODUCTION 

The heat-treating department of the Brown-Lipe-Chapin 
Company, Syracuse, N. Y., runs day and night, and besides 
handling all the hardening of tools, parts of jigs, fixtures, special 
machines and appliances, carburizes and heat-treats every 
month between 150,000 and 200,000 gears, pinions, crosses and 
other components entering into the construction of differentials 
for automobiles. 

The treatment of the steel really begins in the mill, where the 
steel is made to conform to a specific formula. On the arrival 
of the rough forgings at the Brown-Lipe-Chapin factory, the 
first of a long series of inspections begins. 



122 THE WORKING OF STEEL 

Annealing Method. — Forgings which are too hard to machine 
are put in pots with a little charcoal to cause a reducing atmos- 
phere and to prevent scale. The covers are then luted on and the 
pots placed in the furnace. Carbon steel from 15 to 25 points 
is annealed at 1,600°F. Nickel steel of the same carbon and 
containing in addition 3^ per cent nickel is annealed at 1,450°F. 
When the pots are heated through, they are rolled to the yard 
and allowed to cool. This method of annealing gives the best 
hardness for quick machining. 

The requirements in the machine operations are very rigid 
and, in spite of great care and probably the finest equipment of 
special machines in the world, a small percentage of the product 
fails to pass inspection during or at the completion of the machine 
operations. These pieces, however, are not a loss, for they play 
an important part in the hardening process, indicating as they 
do the exact depth of penetration of the carburizing material 
and the condition of both case and core. 

Heat-treating Department. — The heat-treating department 
occupies an L-shaped building. The design is very practical, 
with the furnace and the floor on the same level so that there is 
no lifting of heavy pots. Fuel oil is used in all the furnaces 
and gives highly satisfactory results. The consumption of fuel 
oil is about 2 gal. per hour per furnace. 

The work is packed in the pots in a room at the entrance to the 
heat-treatment building. Before packing, each gear is stamped 
with a number which is a key to the records of the analysis and 
complete heat treatment of that particular gear. Should a 
question at any time arise regarding the treatment of a certain 
gear, all the necessary information is available if the number on 
the gear is legible. For instance, date of treatment, furnace, 
carburizing material, position of the pot in the furnace, position 
of gear in pot, temperature of furnace and duration of treatment 
are all tabulated and tiled for reference. 

After marking, all holes and parts which are to remain un- 
carburized are plugged or luted with a mixture of Kaolin and 
Mellville gravel clay, and the gear is packed in the carburizing 
material. Bohnite, a commercial carburizing compound is 
used exclusively at this plant. This does excellent work and is 
economical. Broadly speaking, the economy of a carburizing 
compound depends on its lightness. The space not occupied by 
work must be filled with compound; therefore, other things being 



HEAT TREATMENT OF STEEL 



123 



equal, a compound weighing 25 lb. would be worth more than 
twice as much as one weighing 60 lb. per cubic foot. It has been 
claimed that certain compounds can be used over and over again, 
but this is only true in a limited way, if good work is required. 
There is, of course, some carbon in the compound after the first 
use, but for first-class work, new compound must be used each 
time. 

The Packing Department. — In Fig. 46 is shown the packing 
pots where the work is packed. These are of malleable cast 
iron, with an internal vertical flange around the hole A. This 
fits in a bell on the end of the cast-iron pipe B, which is luted in 
position with fireclay before the packing begins. At C is shown 




Fig. 46. — Packing department and special pots. 



a pot ready for packing. The crown gears average 10 to 12 in. 
in diameter and weigh about 11 lb. each. When placed in the 
pots, they surround the central tube, which allows the heat to 
circulate. Each pot contains five gears. Two complete scrap 
gears are in each furnace (i.e., one which fails to pass machining 
inspection), and at the top of front pot, are two or more short 
segments of scrap gear, used as test pieces to gage depth. 

After filling the top with compound, the lid D is luted on. 
Ten pots are then placed in a furnace. It will be noted that the 
pots to the right are numbered 1, 2, 3, 4, indicating the position 
they are to occupy in the furnace. 

The cast-iron ball shown at E is small enough to drop through 
the pipe B, but will not pass through the hole A in the bottom of 



124 THE WORKING OF STEEL 

the pot. It is used as a valve to plug the bottom of the pot to 
prevent the carburizing compound from dropping through when 
removing the carburized gears to the quenching bath. 

Without detracting from the high quality of the work, the 
metallurgist in this plant has succeeded in cutting out one entire 
operation and reducing the time in the hardening room by about 
24 hr. 

Formerly, the work was carburized at about 1,700°F. for 9 hr. 
The pots were then run out into the yard and allowed to cool 
slowly. When cool, the work was taken out of the pots, reheated 
and quenched at 1,600°F. to refine the core. It was again 
reheated to 1,425°F. and quenched to refine the case. Finally, 
it was drawn to the proper temper. 

Short Method of Treatment.- — In the new method, the packed 
pots are run into the case-hardening furnaces, which are heated to 
1,600°F. On the insertion of the cold pots, the temperature 
naturally falls. The amount of this fall is dependent upon a 
number of variables, but it averages nearly 500°F. as shown in 
the pyrometer chart, Fig. 51. The work and furnace must be 
brought to 1,600°F. within 2% hr.; otherwise, a longer time will 
be necessary to obtain the desired depth of case. On this work, 
the depth of case required is designated in thousandths, and on 
crown gears, the depth in 0.028 in. Having brought the work 
to a temperature of 1,600°F. the depth of case mentioned can 
be obtained in about 5}^ hr- by maintaining this temperature. 

As stated before, at the top of each pot are several test pieces 
consisting of a whole scrap gear and several sections. After the 
pots have been heated at 1,600°F. for about 5^ hr., they are 
removed, and a scrap-section test-piece is quenched direct from 
the pot in mineral oil at not more than 100°F. The end of a tooth 
of this is then ground and etched to ascertain the depth of case. 
As these test pieces are of exactly the same cross-section as the 
gears themselves, the carburizing action is similar. When the 
depth of case has been found from the etched test pieces to be 
satisfactory, the pots are removed. The iron ball then is dropped 
into the tube to seal the hole in the bottom of the pot; the cover 
and the tube are removed, and the gears quenched direct from 
the pot in mineral oil, which is kept at a temperature not higher 
than 100°F. 

The Effect. — The heating at 1,600°F. gives the first heat treat- 
ment which refines the core, which under the former high heat 



HEAT TREATMENT OF STEEL 125 

(1,700°E) was rendered coarsely crystalline. All the gears, 
including the scrap gears, are quenched direct from the pot in this 
manner. 

The gears then go to the reheating furnaces, situated in front 
of a battery of Gleason quenching machines. These furnaces 
accommodate from 12 to 16 crown gears. The carbon-steel gears 
are heated in a reducing atmosphere to about 1,425°R (depending 
on the carbon content) placed in the dies in the Gleason quench- 
ing machine, and quenched between dies in mineral oil at less 
than 100°F. The test gear receives exactly the same treatment as 
the others and is then broken, giving a record of the condition of 
both case and core. 

Affinity of Nickel Steel for Carbon. — The carbon- and nickel- 
steel gears are carburized separately owing to the difference in 
time necessary for their carburization. Practically all printed 
information on the subject is to the effect that nickel steel takes 
longer to carburize than plain carbon steel. This is directly op- 
posed to the conditions found at this plant. For the same depth 
of case, other conditions being equal, a nickel-steel gear would 
require from 20 to 30 min. less than a low carbon-steel gear. 

From the quenching machines, the gears go to the sand-blast- 
ing machines, situated in the wing of the heat-treating building, 
where they are cleaned. From here they are taken to the testing 
department. The tests are simple and at the same time most 
thorough. 

Testing and Inspection of Heat Treatment. — The hard parts of 
the gear must be so hard that a new mill file does not bite in the 
least. Having passed this file test at several points, the gears go 
to the center-punch test. The inspector is equipped with a 
wooden trough secured to the top of the bench to support the gear, 
a number of center punches (made of %-in. hex-steel having 
points sharpened to an angle of 120 deg.) and a hammer weighing 
about 4 oz. With these simple tools, supplemented by his skill, 
the inspector can feel the depth and quality of the case and the 
condition of the core. The gears are each tested in this way at 
several points on the teeth and elsewhere, the scrap gear being 
also subjected to the test. Finally, the scrap gear is securely 
clamped in the straightening press shown in Fig. 47. With a 
33^-lb. hammer and a suitable hollow-ended drift manipulated 
by one of Sandow's understudies, teeth are broken out of the 
scrap gear at various points. These give a record confirming 



126 



THE WORKING OF STEEL 



the center-punch tests, which, if the angle of the center punch is 
kept at 120 deg. and the weight of the hammer and blow are uni- 
form, is very accurate. 

After passing the center-punch test the ends of the teeth are 
peened lightly with a hammer. If they are too hard, small 
particles fly off. Such gears are drawn in oil at a temperature of 
from 300 to 350°F., depending on their hardness. Some builders 
prefer to have the extreme outer ends of the teeth drawn some- 
what lower than the rest. This drawing is done on gas-heated 
red-hot plates, as shown at A in Fig. 48. 




Fig. 47. — -Press for holding test gears for breaking 



Nickel steel, in addition to all the tests given to carbon steel, 
is subjected to a Brinell test. For each steel, the temperature 
and the period of treatment are specific. For some unknown 
reason, apparently like material with like treatment will, in iso- 
lated cases, not produce like results. It then remains for the 
treatment to be repeated or modified, but the results obtained 
during inspection form a valuable aid to the metallurgist in 
determining further treatment. 



HEAT TREATMENT OF STEEL 



127 



Temperature Recording and Regulation. — Each furnace is 
equipped with pyrometers, but the reading and recording of all 
temperatures are in the hands of one man, who occupies a room 
with an opening into the end of the hardening department. The 
opening is about 15 ft. above the floor level. On each side of it, 
easily legible from all of the furnaces, is a board with the numbers 
of the various furnaces, as shown in Figs. 49 and 50. Opposite 
each furnace number is a series of hooks whereon are hung 
metal numbers representing the pyrometer readings of the 
temperature in that particular furnace. Within the room, as 
shown in Fig. 50, the indicating instrument is to the right, and 
to the left is a switchboard to connect it with the thermo-couples 




Fig. 48. — Gas heated drawing plate for tooth ends. 

in the various furnaces. The boards shown to the right and the 
left swing into the room, which enables the attendant easily to 
change the numbers to conform to the pyrometer readings. 
Readings of the temperatures of the carburizing furnaces are 
taken and tabulated every ten minutes. These, numbered 1 to 
10, are shown on the board to the right in Fig. 49. The card 
shown in Fig. 51 gives such a record. These records are filed 
away for possible future reference. 

The temperatures of the reheating furnaces, numbered from 
11 to 26 and shown on the board to the left in Fig. 49, are taken 
every 5 min. 

Each furnace has a large metal sign on which is marked the 
temperature at which the furnace regulator is required to keep 



128 



THE WORKING OF STEEL 




HEAT TREATMENT OF STEEL 



129 



his heat. As soon as any variation from this is posted on the 
board outside the pyrometer room, the attendant sees it and 
adjusts the burners to compensate. 

Dies for Gleason Tempering Machines. — In Fig. 52 is shown 
a set of dies for the Gleason tempering machine. These accu- 



OBROWN-LIPE-CHAPIN COMPANY y-N 
. METALLURGICAL DEPT. ^ 

/ .fcSSw no kf. DA Tt jJl 4//&T 

iO BUN. TE«P. /^4aRB.J.J X . /3 K**-* 




ZMJL 

DISTRIBUTION OF HEAT HOURS AS PER CLASSES 



n 


2 


3 


4 


s 


6 


7 


S 


9 


10 


II 


12 


13 


14 


15 


16 



Fig. 51. — Carburizing furnace record. 

rately made dies fit and hold the gear true during quenching, 
thus preventing distortion. 

Referring to Fig. 52, the die A has a surface B which fits 
the face of the teeth of the gear C. This surface is perforated by 
a large number of holes which permit the quenching oil to 
circulate freely. The die A is set in the upper end of the plunger 



130 



THE WORKING OF STEEL 



A of the tempering machine, shown in Fig. 53, a few inches above 

the surface of the quench- 
ing oil in the tank TV. 
Inside the die A are the 
centering jaws D, Fig. 54, 
which are an easy fit for 
the bore of the gear C. 
The inner surface of the 
centering jaws is in the 
shape of a female cone. 
The upper die is shown at 
E. In the center (separate 
from it, but a snug sliding 
fit in it) is the expander G, 
which, during quenching, 
enters the taper in the 
centering jaws D, expand- 
ing them against the bore 
of the gear C. The faces 
F of the upper die E fit 
two angles at the back of 
the gear and are grooved 
for the passage of the 
quenching oil. The upper 
die E is secured to the die 
carrier B, shown in Fig. 9, 
and inside the die is the ex- 
pander G, which is backed 
up by compression springs. 
Hardening Operation. — 
Hardening a gear is accom- 
plished as follows : The gear 
is taken from the furnace by 
the furnaceman and placed 
in the lower die, surround- 
ing the centering jaws, as 
shown at H in Fig. 52 and 
C in Fig. 53. Air is then 
turned into the cylinder D, 
and the piston rod E, the die carrier B, the top die F and the 
expander G descend. The pilot H enters a hole in the center of 




HEAT TREATMENT OF STEEL 



131 



-80 to 90 lb. 
Air Pressure 



the lower die, and the expander G enters the centering jaws I, 
causing them to expand and center the gear C in the lower die. 
On further advance of 
the piston rod E, the ex- 
pander G is forced up- 
ward against the pres- 
sure of the springs J 
and the upper die F 
comes in contact with 
the upper surface of the 
gear. Further down- 
ward movement of the 
dies, which now clamp 
the work securely, over- 
comes the resistance of 
the pressure weight K 
(which normally keeps 
up the plunger A), and 
the gear is submerged in 
the oil. The quenching 
oil is circulated through 
a cooling system outside 
the building and enters 
the tempering machine 
through the inlet pipe 
L. When the machine 
is in the position shown, 
the oil passes out through 
the ports M in the lower 
plunger to the outer re- 
servoir N, passing to the 
cooling system by way of 
the overflow 0. When 
the lower plunger A is 
forced downward, the 
ports M are automatic- 
ally closed and the cool 
quenching oil from the 
inlet pipe L, having no other means of escape, passes through 
the holes in the lower die and the grooves the upper, circulat- 
ing in contact with the surfaces of the gear and passes to 




'///MM WWW///////W//WM 

-Gleason tempering machine. 



132 



THE WORKING OF STEEL 



the overflow. When the air pressure is released, the counter- 
weights return the parts to the positions shown in Fig. 53, and 
the operator removes the gear. 

The gear comes out uniformly hard all over and of the same 
degree of hardness as when tempered in an open tank. The 
output of the machine depends on the amount of metal to be 
cooled, but will average from 8 to 16 per hour. Each machine 
is served by one man, two furnaces being required to heat the 
work. A slight excess of oil is used in the firing of the furnaces 
to give a reducing atmosphere and to avoid scale. 




Fig. 54. — Hardening and shrinking sleeves. 

Carburizing Low-carbon Sleeves. — Low-carbon sleeves are 
carburized and pushed on malleable-iron differential-case hubs. 
Formerly, these sleeves were given two treatments after carburi- 
zation in order to refine the case and the core, and then sent to 
the grinding department, where they were ground to a push fit 
for the hubs. After this they were pushed on the hubs. By 
the method now employed, the first treatment refines the core, 
and on the second treatment, the sleeves are pushed on the hub 
and at the same time hardened. This method cuts out the 
internal grinding time, pressing on hubs, and haulage from one 
department to another. Also, less work is lost through splitting 
of the sleeves. 



HEAT TREATMENT OF STEEL 133 

The machine for pushing the sleeves on is shown in Fig. 54. 
At A is the stem on which the hot sleeve B is to be pushed. 
The carburized sleeves are heated in an automatic furnace, 
which takes them cold at the back and feeds them through to 
the front, by which time they are at the correct temperature. 
The loose mandrel C is provided with a spigot on the lower end, 
which fits the hole in the differential-case hub. The upper end 
is tapered as shown and acts as a pilot for the ram D. The 
action of pushing on and quenching is similar to the action of the 
Gleason tempering machine, with the exception that water 
instead of oil is used as a quenching medium. The speed of 
operation depends on a number of variables, but from 350 to 500 
can be heated and pressed on in 11 hr. 

Cyanide Bath for Tool Steels. — All high-carbon tool steels 
are heated in a cyanide bath. With this bath, the heat can be 
controlled within 3 deg. The steel is evenly heated without 
exposure to the air, resulting in work which is not warped and 
on which there is no scale. The cyanide bath is, of course, 
not available for high-speed steel because of the very high 
temperatures necessary. 

DROP FORGING DIES 

The kind of steel used in the die of course influences the heat 
treatment it is to receive, but this also depends on the kind 
of work the die is to perform. If the die is for a forging which is 
machined all over and does not have to be especially close to 
size, where a variation of 3^16 m - is n °t considered excessive, 
a low grade steel will be perfectly satisfactory. 

In cases of fine work, however, where the variation cannot be 
over 0.005 to 0.01 in. we must use a fine steel and prevent its 
going out of shape in the heating and quenching. A high quality 
crucible steel is suggested with about the following analysis: 
Carbon 0.75 per cent, manganese 0.25 per cent, silicon 0.15 per 
cent, sulphur 0.015 per cent, and phosphorus 0.015 per cent. 
Such a steel will have a decalescent point in the neighborhood of 
1,355°F. and for the size used, probably in a die of approximately 
8 in., it will harden around 1,450°F. 

To secure best results care must be taken at every step. The 
block should be heated slowly to about 1,400°F., the furnace 
closed tight and allowed to cool slowly in the furnace itself. 
It should not soak at the high temperature. 



134 THE WORKING OF STEEL 

After machining, and before it is put in the furnace for hard- 
ening, it should be slowly preheated to 800 or 900°F. This can 
be done in several ways, some putting the die block in front of the 
open door of a hardening furnace and keeping the furnace at 
about 1,000°F. The main thing is to heat the die block very 
slowly and evenly. 

The hardening heat should be very slow, 7 hr. being none too 
long for such a block, bringing the die up gradually to the quench- 
ing temperature of 1,450°. This should be held for Y^ hr. or 
even a little more, when the die can be taken out and quenched. 
There should be no guess work about the heating, a good pyro- 
meter being the only safe way of knowing the correct temperature. 

The quenching tank should be of good size and have a spray 
or stream of water coming up near the surface. Dip the die 
block about 3 in. deep and let the stream of water get at the 
face so as to play on the forms. By leaving the rest of the 
die out of the water, moving the die up and down a trifle to 
prevent a crack at the line of immersion, the back of the block 
is left tough while the face is very hard. To overcome the 
tendency to warp the face it is a good plan to pour a little water 
on the back of the die as this tends to even up the cooling. The 
depth to which the die is dipped can be easily regulated by placing 
bars across the tank at the proper depth. 

After the scleroscope shows the die to be properly hardened, 
which means from 98 to 101, the temper should be drawn as 
soon as convenient. A lead pot in which the back of the die can 
be suspended so as to heat the back side, makes a good method. 
Or the die block can be placed back to the open door of a furnace. 
On a die of this size it may take several hours to draw it to the 
desired temper. This can be tested while warm by the sclero- 
scope method, bearing in mind that the reading will not be the 
same as when cold. If the test shows from 76 to 78 while warm, 
the hardness when cold will be about 83, which is about right for 
this work. 

S. A. E. HEAT TREATMENTS 

The Society of Automotive Engineers have adopted certain 
heat treatments to suit different steels and varying conditions. 
These have already been referred to on pages 39 to 41 in 
connection with the different steels used in automobile practice. 
These treatments are designated by letter and correspond with 
the designations in the table. 



HEAT TREATMENT OF STEEL 135 

Heat Treatments 

Heat Treatment A 
After forging or machining : 

1. Carbonize at a temperature be- 2. Gool slowly or quench. 

tween 1,600°F. and 1,750°F. 3. Reheat to 1,450-1,500°F. and 
(1,650-1,700°F. desired.) quench. 

Heat Treatment B 
After forging or machining : 

1. Carbonize between 1,600°F. 4. Quench. 

and 1,750°F. (1,650-1,700°F. 5. Reheat to 1,400-1,450°F. 
desired.) 6. Quench. 

2. Cool slowly in the carbonizing 7. Draw in hot oil at 300 to 450°F., 

mixture. depending upon the degree of 

3. Reheat to 1, 550-1, 625°F. hardness desired. 

Heat Treatment D 
After forging or machining : 

1. Heat to 1,500-1,600°F. 4. Quench. 

2. Quench. 5. Reheat to 600-1, 200°F. and cool 

3. Reheat to 1,450-1,500°F. slowly. 

Heat Treatment E 
After forging or machining : 

1. Heat to 1, 500-1, 550°F. 4. Quench. 

2. Cool slowly. 5. Reheat to 600-1, 200°F. and cool 

3. Reheat to 1,450-1, 500°F. slowly. 

Heat Treatment F 
Af ter shaping or coiling : 

1. Heat to 1,425-1,475°F. 3. Reheat to 400-900°F., in accord- 

2. Quench in oil. ance with temper desired and 

cool slowly. 

Heat Treatment G 
After forging or machining : 

1. Carbonize at a temperature between 1,600°F. and 1,750°F. (1,650- 

1,700°F. desired). 

2. Cool slowly in the carbonizing mixture. 

3. Reheat to 1,500-1,550°F. 

4. Quench. 

5. Reheat to 1,300-1,400°F. 

6. Quench. 

7. Reheat to 250-500°F. (in accordance with the necessities of the case) 

and cool slowly. . 

Heat Treatment H 
After forging or machining : 

1. Heat to 1,500-1,600°F. 

2. Quench. 

3. Reheat to 600-1, 200°F. and cool slowly. 



136 THE WORKING OF STEEL 

Heat Treatment K 
After forging or machining: 

1. Heat to 1,500-1, 550°F. 4. Quench. 

2. Quench. 5. Reheat to 600-l,200°F. and cool 

3. Reheat to 1, 300-1, 400°F. slowly. 

Heat Treatment L 
After forging or machining: 3. Reheat to 1,400-1, 500 0, F. 

1. Carbonize between 1,600°F. 4. Quench. 

and 1,750°F. (1,650-1,700°F. 5. Reheat to 1,300-1,400°F. 
desired). 6. Quench. 

2. Cool slowly in the carbonizing 7. Reheat to 250-500°F. and cool 

mixture. slowly. 

Heat Treatment M 
After forging or machining : 

1. Heat to 1, 450-1, 500°F. 3. Reheat to 500-l,250°F. and cool 

2. Quench. slowly. 

Heat Treatment P 
After forging or machining : 

1. Heat to 1,450-1, 500°F. 4. Quench. 

2. Quench. 5. Reheat to 500-l,250°F. and cool 

3. Reheat to 1,375-1,450°F. slowly. 

Heat Treatment Q 
After forging : 3. Machine. 

1. Heat to 1,475-1,525°F. (Hold 4. Reheat to 1,375-1,425°F. 

at this temperature one-half 5. Quench. 

hour, to insure thorough 6. Reheat to 250-550°F. and cool 

heating.) slowly. 

2. Cool slowly. 

Heat Treatment R 
After forging : 4. Cool slowly. 

1. Heat to 1,500-1,550°F. 5. Machine. 

2. Quench in oil. 6. Reheat to 1,350-1,450°F. 

3. Reheat to 1,200-1,300°F. (Hold 7. Quench in oil. 

at this temperature three 8. Reheat to 250-500°F. and cool 
hours.) slowly. 

Heat Treatment S 
After forging or machining: 3. Reheat to 1, 650-1, 750°F. 

1. Carbonize at a temperature be- 4. Quench. 

tween 1,600 and 1,750°F. 5. Reheat to 1,475-1, 550°F. 
(1,650-1,700°F. desired.) 6. Quench. 

2. Cool slowly in the carbonizing 7. Reheat to 250-550°F. and cool 

mixture. slowly. 

Heat Treatment T 
After forging or machining: 

1. Heat to 1,650-1,750°F. 3. Reheat to 500-1, 300°F. and cool 

2. Quench. slowly. 



HEAT TREATMENT OF STEEL 



137 



Heat Treatment U 
After forging : 3. Machine. 

1. Heat to 1,525-1,600°F. (Hold 4. Reheat to 1, 650-1, 700°F. 

for about one-half hour.) 5. Quench. 

2. Cool slowly. 6. Reheat to 350-550°F. and cool 

slowly. 

Heat Treatment V 

After forging or machining : 

1. Heat to 1, 650-1, 750°F. 3. Reheat to 400-1, 200°F. and cool 

2. Quench. slowly. 



RESTORING OVERHEATED STEEL 

The effect of heat treatment on overheated steel is shown 
graphically in Fig. 55 to the series of illustrations on pages 137 





" \. / ;*» : *>'*>. V,i» l'«<f J J- -»- I 



I «*' & 6* <? rf» «*' 



STRUCTURAL CHANGES 

ON 

HE.ATINQ 8c COOLING MILD STEEL. 




9 10 11 12 13 H 15 IS 17 18 19 20 21 
HOUR 1 : 



Fig. 55. — Chart of changes due to heating and cooling. 

to 144. This was prepared by Thos. Firth & Sons, Ltd., 
Sheffield, England. 

The center piece Fig. 55 represents a block of steel weighing 
about 25 lb. The central hole accommodated a thermo-couple 
which was attached to an autographic recorder. The curve is a 
copy of the temperature record during heating and cooling. Into 
the holes in the side of the block small pegs of overheated mild 
steel were inserted. One peg was withdrawn and quenched at 



138 



THE WORKING OF STEEL 







Fig. 56. — The structure of overheated mild steel from which all the pegs 
were made (magnified 25 diameters). The pegs withdrawn at 720°C, or earlier, 
had this structure and were quite soft. 




Fig. 57. — Peg withdrawn at 750°C. (magnified 25 diameters). The structure 
is apparently unaltered, but the peg was hard and, unlike the earlier ones, would 
not bend double. 



HEAT TREATMENT OF STEEL 



139 




Fig. 58. — A portion of 56 magnified 200 diameters to show that the dark (pearl- 
ite) areas are laminated. 




Fig. 59.- — A portion of 57 magnified 200 diameters, showing that pearlite areas 
are no longerjaminated and providing reason for observed hardness. 



140 



THE WORKING OF STEEL 




Fig. 



60. — Peg withdrawn at 780°C. (magnified 25 diameters), showing inter- 
diffusion of transformed pearlite and ferrite areas. 




Fig. 61. — Peg withdrawn at 800°C. (magnified 25 diameters), showing inter- 
diffusion so far advanced that the original outline of the crystals is now only 
faintly suggested. 



HEAT TREATMENT OF STEEL 



141 




Fig. 62. — Peg withdrawn at 850°C. (magnified 100 diameters) after inter- 
diffusion was completed. Note the regular outlines and the small size of the 
crystals as compared with 57. 




Fig. 63. — To facilitate comparison 57 was enlarged to the same magnification 
as 62, and the one superimposed on the other. The single large crystal occupied 
as much space as 8,000 of the smaller ones. 



142 



THE WORKING OF STEEL 




Fig. 64. — The peg withdrawn on cooling at 800°C. (magnified 100 diameters) 
shows the first reappearance of free ferrite. All pegs withdrawn at higher tem- 
peratures were like Fig. 62. 




Fig. 65.- 



-Peg withdrawn after cooling to 760°C. The increased amount of free 
ferrite arranges itself about the crystals as envelopes. 



HEAT TREATMENT OF STEEL 



143 




Fig. 66. — Peg withdrawn after cooling to 740°C. 



ill 






;^ 



iiVlKScsL 



ft >Sv.<VJttifc/ 



;%C^' 





Fig. 67. — Peg withdrawn after cooling to 670°C. (magnified 800 diameters). 
Just at this moment the lamination of pearlite, which now occupied its original 
area, was taking place. In some parts the lamination was perfect, in other 
parts the iron and iron-carbide were still dissolved in each other. 



144 



THE WORKING OF STEEL 



each of the temperatures indicated by the numbered arrows, and 
after suitable preparation these pegs were photographed in 
order to show the changes in structure taking place during heating 
and cooling operations. The illustrations here reproduced are 




Fig. 68. — Any peg withdrawn after 670°C. on cooling (magnified 100 diameters). 



Fig 69 




selected from those photographs with the object of presenting 
pictorially the changes involved in the refining of overheated 
steel or steel castings. Figures 56 to 69 with their captions, 
show much that is of value to steel users. 



CHAPTER IX 
HARDENING CARBON STEEL FOR TOOLS 

For years the toolmaker had full sway in regard to make of 
steel wanted for shop tools, he generally made his own designs, 
hardened, tempered, ground and usually set up the machine 
where it was to be used and tested it. 

Most of us remember the toolmaker during the sewing machine 
period when interchangeable tools were beginning to find their 
way; rather cautiously at first. The bicycle era was the real 
beginning of tool making from a manufacturing standpoint, 
when interchangeable tools for rapid production were called for 
and toolmakers were in great demand. Even then, jigs, and 
fixtures were of the toolmaker's own design, who practically 
built every part of it from start to finish. 

The old way, however, had to be changed. Instead of the 
toolmaker starting his work from cutting off the stock in the old 
hack saw, a place for cutting off stock was provided. If, for 
instance, a forming tool was wanted, the toolmaker was given 
the master tool to make while an apprentice roughed out the 
cutter. The toolmaker, however, reserved the hardening process 
for himself. That was one of the particular operations that the 
old toolmaker refused to give up. It seemed preposterous to 
think for a minute that any one else could possibly do that parti- 
cular job without spoiling the tools, or at least warp it out of 
shape (most of us did not grind holes in cutters 15 to 20 years 
ago) ; or a hundred or more things might happen unless the tool- 
maker did his own hardening and tempering. 

That so many remarkably good tools were made at that time 
is still a wonder to many, when we consider that the large shop 
had from 30 to 40 different men, all using their own secret com- 
pounds, heating to suit eyesight, no matter if the day was bright 
or dark, and then tempering to color. But the day of the old 
toolmaker has changed. Now a tool is designed by a tool 
designer, O.K.'d, and then a print goes to the foreman of the 
tool department, who specifies the size and gets the steel from 
the cutting-off department. After finishing the machine work 
10 145 



146 THE WORKING OF STEEL 

it goes to the hardening room, and this is the problem we shall 
now take up in detail. 

The Modern Hardening Room. — A hardening room of today 
means a very different place from the dirty, dark smithshop in 
the corner with the open coal forge. There, when we wanted to be 
somewhat particular, we sometimes shoveled the coal cinders to one 
side and piled a great pile of charcoal on the forge. We now 
have a complete equipment; a gas- or oil-heating furnace, good 
running water, several sizes of lead pots, and an oil tank large 
enough to hold a barrel of oil. By running water, we mean a large 
tank with overflow pipes giving a constant supply. The ordi- 
nary hardening room equipment should consist of : 

Gas or oil muffle furnace for hardening. 

Gas or oil forge furnace. 

A good size gas or oil furnace for annealing and case-hardening. 

A gas or oil furnace to hold lead pots. 

Oil tempering tank, gas- or oil-heated. 

Pressure blower. 

Large oil tank to hold at least a barrel of oil. 

Big water tank with screen trays connected with large pipe from bottom 
with overflow. 

Straightening press. 

The furnace should be connected with pyrometers and tempering tank 
with a thermometer. 

Beside all this you need a good man. It does not make much 
difference how completely the hardening department is fitted 
up, if you expect good work, a small percentage of loss and to be 
able to tackle anything that comes along, you must have a good 
man, one who understands the difference between low- and high- 
carbon steel, who knows when particular care must be exercized 
on particular work. In other words, a man who knows how his 
work should be done, and has the intelligence to follow directions 
on treatments of steel on which he has had no experience. 

Jewelers' tools, especially for silversmith's work, probably have 
to stand the greatest punishment of any all steel tools and to 
make a spoon die so hard that it will not sink under a blow from 
an 1,800-lb. hammer with a 4-ft. drop, and still not crack, de- 
mands careful treatment. 

To harden such dies, first cover the impression on the die with 
paste made from bone dust or lampblack and oil. Place face 
down in an iron box partly filled with crushed charcoal, leaving 
back of die uncovered so that the heat can be seen at all times. 



HARDENING CARBON STEEL FOR TOOLS 



147 



Heat slowly in furnace to a good cherry red. The heat depends 
on the quality and the analysis of steel and the recommended 



\W 



w amm m 



mmm 



lllfi 




w 



wm 



rM. 



Fig. 70. — Quenching a die, face down. 

actions of the steel maker should be carefully followed. When 
withdrawn from the fire the die should be quenched as shown in 
Fig. 70 with the face of die down 
and the back a short distance out 
of the water. When the back is 
black, immerse all over. 

If such a tank is not at hand, it 
would pay to rig one up at once, 
although a barrel of brine may be 
used, or the back of the die may be 
first immersed to a depth of about 
% in. When the piece is immersed, 
hold die on an angle as in Fig. 71. 

This is for the purpose of expell- 
ing all steam bubbles as they form 
in contact with hot steel. We are 
aware of the fact that a great many 
toolmakers in jewelry shops still 

cling to the overhead bath, as in Fig. 72, but more broken pieces 
and more dies with soft spots are due to this method than to all 
the others combined, as the water strikes one spot in force, con- 




-Hold die at angle 
quench. 



148 



THE WORKING OF STEEL 



tracting the surface so much faster than the rest of the die that 
the results are the same as if an uneven heating had been given 
the steel. 

Take Time for Hardening. — Uneven heating and poor quench- 
ing has caused loss of many very valuable dies, and it certainly 
seems that when a firm spends from $75 to $450 in cutting a die 
that a few hours could be spared for'proper hardening. But the 
usual feeling is that a tool must be hurried as soon as the hard- 
ener gets it, and if a burst die is the result from either uneven or 
overheated steel and quenching same without judgment, the 
steel gets the blame. 




/ 




M, 
^ 




/ / 













Fig. 72. — An obsolete method. 

Give the steel a chance to heat properly, mix a little common 
sense with "your 30 years experience on the other fellows steel." 
Remember that high-carbon steel hardens at a lower heat than 
low-carbon steel, and quench when at the right heat in the two 
above ways, and 99 per cent of the trouble will vanish. 

When a die flies to pieces in quenching, don't rush to the super- 
intendent with a "poor-steel" story, but find out first why it 
broke so that the salesman who sold it will not be able to harden 
piece after piece from the same bar satisfactorily. If you find 
a "cold short," commonly called "a pipe," you can laythe blame 
on the steelmaker. If it is a case of overheating and quenching 



HARDENING CARBON STEEL FOR TOOLS 149 

when too hot, you will find a coarse grain with many bright spots 
like crystals to the hardening depth. If uneven heating is the 
cause, you will find a wider margin of hardening depth on one 
side than on the other, or find the coarse grain from over-heating 
on one side while on the other you will find a close grain, which 
may be just right. If you find any other faults than a "pipe," 
or are not able to harden deep enough, then take the blame like 
a man and send for information. The different steel salesmen are 
good fellows and most of them know a thing or two about their 
own business. 

For much work a cooling bath at from 50 to 75°F. is very good 
both for small hubs, dies, cutter plates or plungers, will harden 
best in a barrel of brine, but if running cold water is at hand, 
splendid results will be obtained.. Cutter plates should always 
be dipped corner first and if any have stripper holes, they should 
first be plugged with asbestos or fire clay cement. 

In general it may be said that the best hardening temperature 
for carbon steel is the lowest temperature at which it will harden 
properly. 

CARBON IN TOOL STEEL 

Carbon tool steel, or "tool steel" as it is commonly called, 
usually contains from 80 to 125 points (or from 0.80 to 1.25 per 
cent) of carbon, and none of the alloy which go to make up the 
high speed steels. This was formerly known also as crucible or 
"cast" steel, or crucible cast steel, from the way in which it was 
made. This was before the days of steel castings. The advent 
of these caused so much confusion that the term was soon dropped. 
When we say "tool steel, " we nearly always refer to carbon-tool 
steel, high-speed steel being usually designated by that name. 

For many purposes carbon-steel cutters are still found best, 
although where a large amount of material is to be removed at a 
rapid rate, it has given way to high-speed steels. 

CARBON STEELS FOR DIFFERENT TOOLS 

All users of tool steels should carefully study the different 
qualities of the steels they handle. Different uses requires 
different kinds of steel for best results, and for the purpose of 
designating different steels some makers have adopted the two 
terms "temper," and "quality," to distinguish between them. 

In this case temper means the percentage of carbon which 



150 THE WORKING OF STEEL 

is combined with the iron to make the metal into a steel. The 
quality means the absence of phosphorous, sulphur and other 
impurities, these depending on the ores and the methods of 
treatment. 

Steel makers have various ways of designating carbon steels 
for different purposes. Some of these systems involve the 
use of numbers, that of the Latrobe Steel Company being given 
herewith. It will be noted that the numbers are based on 20 
points of carbon per unit. The names given the different tem- 
pers are also of interest. Other makers use different numbers. 
The temper list follows : 

Latrobe Temper List of Carbon Tool Steels 
No. 3 temper 0.60 to 0.69 per cent carbon 
No. 3% temper 0-70 to 0.79 per cent carbon 
No. 4 temper 0.80 to 0.89 per cent carbon 
No. 43^2 temper . 90 to . 99 per cent carbon 
No. 5 temper 1 .00 to 1 .09 per cent carbon 
No. 5% temper 1 . 10 to 1.19 per cent carbon 
No. 6 temper 1 . 20 to 1 . 29 per cent carbon 
No. 63^ temper 1 . 30 to 1 . 39 per cent carbon 
No. 7 temper 1 . 40 to 1 . 49 per cent carbon 

Uses of the Various Tempers of Carbon Tool Steel 

Die Temper. — No. 3: All kinds of dies for deep stamping, pressing and 
drop forgings. Mining drills to harden only. Easily weldable. 

Smiths' Tool Temper. — No. 3J^: Large punches, minting and rivet dies, 
nailmakers' tools, hammers, hot and cold sates, snaps and boilermakers' 
tools, various smiths' tools, large shear blades, double handed chisels, caulk- 
ing tools, heading dies, masons' tools and general welding purposes. 

Shear Blade Temper. — No. 4: Punches, large taps, screwing dies, shear 
blades, table cutlery, circular and long saws, heading dies. Weldable. 

General Purpose Temper. — No. 4%: Taps, small punches, screwing dies, 
sawwebs, needles, etc., and for all general purposes. Weldable. 

Axe Temper. — No. 5: Axes, chisels, small taps, miners' drills and jumpers 
to harden and temper, plane irons. Weldable with care. 

Cutlery Temper. — No. 5K : Large milling cutters, reamers, pocket cutlery, 
wood tools, short saws, granite drills, paper and tobacco knives. Weldable 
with very great care. 

Tool Temper . — No. 6: Turning, planing, slotting, and shaping tools, 
twist drills, mill picks, scythes, circular cutters, engravers' tools, surgical 
cutlery, circular saws for cutting metals, bevel and other sections for turret 
lathes. Not weldable. 

Hard Tool Temper. — No. 6^: Small twist drills, razors, small and intri- 
cate engravers' tools, surgical instruments, knives. Not weldable. 

Razor Temper. — No. 7: Razors, barrel boring bits, special lathe tools for 
turning chilled rolls. Not weldable. 






HARDENING CARBON STEEL FOR TOOLS 151 

STEEL FOR CHISELS AND PUNCHES 

The highest grades of carbon or tempering steels are not 
recommended for tools which have to withstand shocks, such 
as for cold chisels or punches. These steels are, however, particu- 
larly useful where it is necessary to cut tempered or heat-treated 
steel which is more than ordinarily hard, for cutting chilled 
iron, etc. They are useful for boring, for rifle-barrel drilling, 
for fine finishing cuts, for drawing dies for brass and copper, for 
blanking dies for hard materials, for formed cutters on automatic 
screw machines and for roll-turning tools. 

Steel of this kind, being very dense in structure, should be 
given more time in heating for forging and for hardening, than 
carbon steels of a lower grade. For forging it should be heated 
slowly and uniformly to a bright red and only light blows used 
as the heat dies out. Do not hammer at all at a black heat. 
Reheat slowly to a dark red for hardening and quench in warm 
water. Grind on a wet grindstone. 

Where tools have to withstand shocks and vibration, as in 
pneumatic hammer work, in severe punching duty, hot or cold 
upsetting or similar work, tool steels containing vanadium or 
chrome-vanadium give excellent results. These are made 
particularly for work of this kind. 

CHISELS— SHAPES AND HEAT TREATMENT 1 

In the chief mechanical engineer's department of the Midland 
Ry., after considerable experimenting, it was decided to order 
chisel steel to the following specifications: carbon, 0.75 to 0.85 
per cent, the other constituents being normal. This gives a 
complete analysis as follows: carbon, 0.75 to 0.85; manganese, 
0.30; silicon, 0.10; sulphur, 0.025; phosphorus, 0.025. 

The analysis of a chisel which had given excellent service was 
as follows: carbon, 0.75; manganese, 0.38; silicon, 0.16; sulphur, 
0.028; phosphorus, 0.026. The heat treatment is unknown. 

At the same time that chisel steel was standardized, the form 
of the chisels themselves was revised, and a standard chart of 
these as used in the locomotive shops was drawn up. Figure 73 
shows the most important forms, which are made to stock orders 

1 Abstract of paper by Henry Fowler, chief mechanical engineer of the 
Midland Ry., England, before the Institution of Mechanical Engineers. 



152 



THE WORKING OF STEEL 



in the smithy and forwarded to the heat-treatment room where 
the hardening and tempering is carried out on batches of fifty. 
A standard system of treatment is employed, which to a very 
large extent does away with the personal element. Since the 




HEAVY BRASS WORK 



•DIAMOND POINT 




CYLINDER REPAIRS (RIGHT HAND) 

k — 2-- 



ROUND NOSE 




6IDE TOOL. (RIGHT HAND) 

\* 3- — H 







SQUARE NOSE 




Fig. 73. — Forms of chisels standardized for the locomotive shops of the Midland 

Ry., England. 

chemical composition is more or less constant, the chief variant 
is the section which causes the temperatures to be varied slightly. 
The chisels are carefully heated in a gas-fired furnace to a tem- 
perature of from 730 to 740°C. (1,340 to 1,364°F.) according to 
section. In practice, the first chisel, is heated to 730°C; and 



HARDENING CARBON STEEL FOR TOOLS 153 

the second to 735°C. (1,355°F.); and a 1 in. half round chisel to 
740 & C, because of their varying increasing thickness of section 
at the points. Upon attaining this steady temperature, the 
chisels are quenched to a depth of % to % in. from the point in 
water, and then the whole chisel is immersed and cooled off in a 
tank containing linseed oil. 

The oil-tank is cooled by being immersed in a cold-water tank 
through which water is constantly circulated. After this treat- 
ment, the chisels have a dead hard point and a tough or sorbitic 
shaft. They are then tempered or the point "let down." This 
is done by immersing them in another oil-bath which has been 
raised to about 215°C. (419°F). The first result is, of course, to 
drop the temperature of the oil, which is gradually raised to its 
initial point. On approaching this temperature the chisels are 
taken out about every 2°C. rise and tested with a file, and at a 
point between 215 and 220°C. (428°F.), when it is found that the 
desired temper has been reached, the chisels are removed, cleaned 
in sawdust, and allowed to cool in an iron tray. 

No comparative tests of these chisels with those bought and 
treated by the old rule-of-thumb methods have been made, as 
no exact method of carrying out such tests mechanically, other 
than trying the hardness by the Brinell or scleroscope method, 
are known; any ordinary test depends so largely upon the dex- 
terity of the operator. The universal opinion of foremen and 
those using the chisels as to the advantages of the ones receiving 
the standard treatment described is that a substantial improve- 
ment has been made. The chisels were not "normalized." 
Tests of chisels normalized at about 900°C. (1,652°F.) showed 
that they possessed no advantage. 

Tools or pieces which have holes or deep depressions should be 
filled before heating unless it is necessary to have the holes hard 
on the inside. In that case the filling would keep the water 
away from the surface and no hardening would take place. 
Where filling is to be done, various materials are used by different 
hardeners. Fireclay and common putty seem to be favored by 
many. 

Every mechanic who has had anything to do with the harden- 
ing of tools knows how necessary it is to take a cut from the 
surface of the bar that is to be hardened. The reason is that in 
the process of making the steel its outer surface has become decar- 
bonized. This change makes it low-carbon steel, which will of 



154 THE WORKING OF STEEL 

course not harden. It is necessary to remove from }{ q to 34 in. 
of diameter on bars ranging from % to 4 in. 

This same decarbonization occurs if the steel is placed in the 
forge in such a way that unburned oxygen from the blast can get 
at it. The carbon is oxidized, or burned out, converting the 
outside of the steel into low-carbon steel. The way to avoid this 
is to use a deep fire. Lack of this precaution is the cause of much 
spoiled work, not only because of decarbonization of the outer 
surface of the metal, but because the cold blast striking the hot 
steel acts like boiling hot water poured into an ice-cold glass 
tumbler. The contraction sets up stresses that result in cracks 
when the piece is quenched. 

PREVENTING DECARBONIZATION OF TOOL STEEL 

It is especially important to prevent decarbonization in such 
tools as taps and form cutters, which must keep their shape after 
hardening and which cannot be ground away on the profile. For 
this reason it is well to put taps, reamers and the like into pieces 
of pipe in heating them. The pipe need be closed on one end 
only, as the air will not circulate readily unless there is an open- 
ing at both ends. 

Even if used in connection with a blacksmith's forge the lead 
bath has an advantage for heating tools of complicated shapes, 
since it is easier to heat them uniformly and they are submerged 
and away from the air. The lead must be stirred frequently 
or the heat is not uniform in all parts of the lead bath. Covering 
the lead with powdered charcoal will largely prevent oxidization 
and waste of lead. 

Such a bath is good for temperatures between 620 and 1,150°F. 
At higher temperatures there is much waste of lead. 

ANNEALING TO RELIEVE INTERNAL STRESSES 

Work quenched from a high temperature and not afterward 
tempered will, if complex in shape, contain many internal stresses 
which may later cause it to break. They may be eased off by 
slight heating without materially lessening the hardness of the 
piece. One way to do this is to hold the piece over a fire and test 
it with a moistened finger. Another way is to dip the piece in 
boiling water after it has first been quenched in a cold bath. 



HARDENING CARBON STEEL FOR TOOLS 155 

Such steps are not necessary with articles which will afterward 
be tempered and in which the strains are thus reduced. 

In annealing steels the operation is similar to hardening, as 
far as heating is concerned. The critical temperatures are the 
proper ones for annealing as well as hardening. From this 
point on there is a difference, for annealing consists in cooling 
as slowly as possible. The slower the cooling the softer will be 
the steel. 

Annealing may be done in the open air, in furnaces, in hot 
ashes or lime, in powdered charcoal, in burnt bone, in charred 
leather and in water. Open-air annealing will do as a crude 
measure in cases where it is desired to take the internal stresses 
out of a piece. Care must be taken in using this method that 
the piece is not exposed to drafts or placed on some cold substance 
that will chill it. Furnace annealing is much better and consists 
in heating the piece in a furnace to the critical temperature and 
then allowing the work and the furnace to cool together. 

When lime or ashes are used as materials to keep air away from 
the steel and retain the heat, they should be first heated to make 
sure that they are dry. Powdered charcoal is used for high-grade 
annealing, the piece being packed in this substance in an iron box 
and both the work and the box raised to the critical temperature 
and then allowed to cool slowly. Machinery steel may be 
annealed in spent ground-bone that has been used in caseharden- 
ing; but tool steel must never be annealed in this way, as it will be 
injured by the phosphorus contained in the bone. Charred 
leather is the best annealing material for high-carbon steel, 
because it prevents decarbonizing taking place. 

WATER ANNEALING 

Water annealing consists in heating the piece, allowing it to 
cool in air until it loses its red heat and becomes black and then 
immediately quenching it in water. This plan works well for 
very low-carbon steel ; but for high-carbon steel what is known as 
the "double annealing treatment" must be given, provided results 
are wanted quickly, as is usually the case with water- or oil-bath 
annealing. The process consists of quenching the steel in water 
or oil, as in hardening, and then reheating it to just below the 
critical point and again quenching it in oil. This process retains 
in the steel a fine-grain structure combined with softness. Large 
pieces of steel should be rough-turned before annealing. 



156 THE WORKING OF STEEL 

QUENCHING TOOL STEEL 

To secure proper hardness, the cooling or quenching of steel is 
as important as its heating. Quenching baths vary in nature, 
there being a large number of ways to cool a piece of steel in 
contrast to the comparatively few ways of heating it. 

Plain water, brine and oil are the three most common quench- 
ing materials. Of these three the brine will give the most hard- 
ness, and plain water and oil come next. The colder that any 
of these baths is when the piece is put into it the harder will be 
the steel; but this does not mean that it is a good plan to dip the 
heated steel into a tank of ice water, for the shock would be so 
great that the bar would probably fly to pieces. In fact, the 
quenching bath must be sometimes heated a bit to take off the 
edge of the shock. 

Brine solutions will work uniformly, or give the same degree 
of hardness, until they reach a temperature of 150°F. above which 
their grip relaxes and the metals quenched in them become softer. 
Plain water holds its grip up to a temperature of approximately 
100°F.; but oil baths, which are used to secure a slower rate of 
cooling, may be used up to 500° or more. A compromise is 
sometimes effected by using a bath consisting of an inch or two of 
oil floating on the surface of water. As the hot steel passes 
through the oil, the shock is not as severe as if it were to be thrust 
directly into the water; and in addition, oil adheres to the tool 
and keeps the water from direct contact with the metal. 

The old idea that mercury will harden steel more than any 
other quenching material has been exploded. A bath consisting 
of melted cyanide of potassium is useful for heating fine engraved 
dies and other articles that are required to come out free from 
scale. One must always be careful to provide a hood or exhaust 
system to get rid of the deadly fumes coming from the cyanide 
pot. 

The one main thing to remember in hardening tool steel is to 
quench on a rising heat. This does not mean a rapid heating as a 
slow increase in temperature is much better in every way. 

The Theory of Tempering. — Steel that has been hardened is 
generally harder and more brittle than is necessary, and in order 
to bring it to the condition that meets our requirements a treat- 
ment called tempering is used. This increases the toughness 
of the steel, i.e., decrease the brittleness at the expense of a 
slight decrease in hardness. 



HARDENING CARBON STEEL FOR TOOLS 157 

There are several theories to explain this reaction, but generally 
it is only necessary to remember that in hardening we quench 
steel from the austenite phase, and, due to this rapid cooling, the 
normal change from austenite to the eutectoid composition does 
not have time to take place, and as a consequence the steel exists 
in a partially transformed and unstable condition at ordinary 
atmospheric temperatures. But owing to the strains and rigid- 
ity set up by this rapid cooling the steel is unable to change into 
its more stable phase until these strains are removed by the ap- 
plication of heat. The higher the heat, the greater the trans- 
formation into the softer phases. As the transformation takes 
place, a certain amount of heat of reaction, which under slow 
cooling would have been released in the critical range, is now 
released and helps to cause a further reaction, the result of which 
is that if a piece of steel is heated to a certain temperature and 
held there, the tempering color, instead of remaining unchanged 
at this temperature, will advance in the tempering-color scale 
as it would with increasing temperature. This means that the 
tempering colors do not absolutely correspond to the tempera- 
tures of steels, but the variations are so slight that we can use 
them in actual practice. 

Temperatures to use. As soon as the temperature of the steel 
reaches 100°C. (212°F.) the transformation begins, increasing 
in intensity as the temperature is raised, until finally when the 
lower critical range is reached, the steel has been all changed into 
the ordinary constituents of unhardened steels. 

If a piece of polished steel is heated in an ordinary furnace, a 
thin film of oxides will form on its surface. The colors of this 
film change with temperature, and so, in tempering, they are gen- 
erally used as an indication of the temperature of the steel. The 
steel should have at least one polished face so that this film of 
oxides may be seen. 

An alternative method to the determination of temper by 
color is to temper by heating in an oil or salt bath. Oil baths 
can be used up to temperatures of 500°F. ; above this, fused-salt 
baths are required. The article to be tempered is put into the 
bath, brought up to and held at the required temperature for a 
certain length of time, and then cooled, either rapidly or slowly. 
This takes longer than the color method, but with low tempera- 
tures the results are more satisfactory, because the temperature 
of the bath can be controlled with a pyrometer. The tempering 



158 



THE WORKING OF STEEL 



temperatures given in the following table are taken from a hand- 
book issued by the Midvale Steel Company. 



Table 23. — Tempering Temperatures for Steels 



Temperature 




Temperature 




for 1 hr. 




for 8 


min. 








Color 






Uses 


Deg. F. 


Deg. C. 


Deg. F. 


Deg. C. 




370 


188 


Faint yellow 


460 


238 


Scrapers, brass-turning 
tools, reamers, taps, mill- 
ing cutters, saw teeth. 


390 


199 


Light straw 


510 


265 


Twist drills, lathe tools, 
planer tools, finishing tools 


410 


210 


Dark straw 


560 


293 


Stone tools, hammer faces, 
chisels for hard work, bor- 
ing cutters. 


430 


221 


Brown 


610 


321 


Trephining tools, stamps. 


450 


232 


Purple 


640 


337 


Cold chisels for ordinary 
work, carpenters' tools, 
picks, cold punches, shear 
blades, slicing tools, slot- 
ter tools. 


490 


254 


Dark blue 


660 


349 


Hot chisels, tools for hot 
work, springs. 


510 


265 


Light blue 


710 


376 


Springs, screw drivers. 



It will be noted that two sets of temperatures are shown, one 
being specified for a time interval of 8 min. and the other for 1 
hr. For the finest work the longer time is preferable, while for 
ordinary rough work 8 min. is sufficient, after the steel has 
reached the specified temperature. 

The rate of cooling after tempering seems to be immaterial, and 
the piece can be cooled at any rate, providing that in large pieces 
it is sufficiently slow to prevent strains. 

Knowing What Takes Place. — How are we to know if we have 
given a piece of steel the very best possible treatment? 

The best method is by microscopic examination of polished and 
etched sections, but this requires a certain expense for laboratory 
equipment and upkeep, which may prevent an ordinary com- 
mercial plant from attempting such a refinement. It is highly 
recommended that any firm that has any large amount of heat 
treatment to do, install such an equipment, which can be pur- 



HARDENING CARBON STEEL FOR TOOLS 159 

chased for from $250 to $500. Its intelligent use will save its 
cost in a very short time. 

The other method is by examination of fractures of small test 
bars. Steel heated to its correct temperatures will show the 
finest possible grain, whereas underheated steel has not had its 
grain structure refined sufficiently, and so will not be at its best. 
On the other hand, overheated steel will have a coarser structure, 
depending on the extent of overheating. 

To determine the proper quenching temperature of any particu- 
lar grade of steel it is only necessary to heat pieces to various 
temperatures not more than 20°C. (36°F.) apart, quench in water, 
break them, and examine the fractures. The temperature 
producing the finest grain should be used for annealing and 
hardening. 

Similarly, to determine tempering temperatures, several pieces 
should be hardened, then tempered to various degrees, and cooled 
in air. Samples, say six, reheated to temperatures varying by 
100° from 300 to 800°C. will show a considerable range of proper- 
ties, and the drawing temperature of the piece giving the desired 
results can be used. 

For drawing tempers up to 500°F. oil baths of fresh cotton seed 
oil can be safely and satisfactorily used. For higher temperature 
a bath of some kind of fused salt is recommended. 

HINTS FOR TOOL STEEL USERS 

Do not hesitate to ask for information from the maker as to the 
best steel to use for a given purpose, mentioning in as much 
detail as possible the use for which it is intended. 

Do not heat the steel to a higher degree than that fixed in the 
description of each class. Never heat the steel to more than a 
faint red without immediately forging it. Heating steel opens 
and coarsens the grain which can only be restored by forging or 
by sudden cooling as in hardening. 

Let the forging begin as soon as the steel is hot enough and 
never let tool steel soak in the fire. Continue the hammering 
vigorously and constantly, using lighter blows as it cools off, and 
stopping when the heat becomes a very dull red or a faint brown. 

Should welding be necessary care should be taken not to 
overheat in order to make an easy weld. Keep it below the 
sparkling point as this indicates that the steel is burnt. 

Begin to forge as soon as the welds are put together taking 



160 THE WORKING OF STEEL 

care to use gentle strokes at first increasing them as the higher 
heat falls, but not overdoing the hammering when the steel 
cools. The hammering should be extended beyond the welding 
point and should continue until the dull red or brown heat is 
reached. 

PREVENTING CRACKS IN HARDENING 

The blacksmith in the small shop, where equipment is usually 
very limited, often consisting of a forge, a small open hard-coal 
furnace, a barrel of water and a can of oil must have skill and 
experience. With this equipment the smith is expected to, and 
usually can, produce good results if proper care is taken. 

In hardening carbon tool steel in water, too much cannot be 
said in favor of slow, careful heating, nor against overheating 
if cracks are to be avoided. 

It is not wise to take the work from the hardening bath and 
leave it exposed to the air if there is any heat left in it, because it 
is more liable to crack than if left in the bath until cold. In 
heating, plenty of time is taken for the work to heat evenly clear 
through, thus avoiding strains caused by quick and improper 
heating. In quenching in water, contraction is much more 
rapid than was the expansion while heating, and strains begin 
the moment the work touches the water. If the piece has any 
considerable size and is taken from the bath before it is cold 
and allowed to come to the air, expansion starts again from the 
inside so rapidly that the chilled hardened surface cracks before 
the strains can be relieved. 

Many are most successful with the hardening bath about blood 
warm. When the work that is being hardened is nearly cold, it is 
taken from the water and instantly put into a can of oil, where 
it is allowed to finish cooling. The heat in the body of the tool 
will come to the surface more slowly, thus relieving the strain 
and overcoming much of the danger of cracking. 

Some contend that the temper should be drawn as soon as 
possible after hardening: but that if this cannot be done for some 
hours, the work should be left in the oil until the tempering can 
be done. It is claimed that forming dies and punch-press dies 
that are difficult to harden will seldom crack if treated in this way. 

Small tools or pieces that are very troublesome because of 
peculiar shape may be hardened in a bath composed of 1 lb. 
corrosive sublimate, 3^2 gal. vinegar and 3^ bbl. rainwater at a 
much lower heat than is required for clear water, the temper to be 



HARDENING CARBON STEEL FOR TOOLS 161 

drawn in the usual way. This bath should be warmed the same 
as the water, and the work hardened in it should be also put in 
the oil. This solution works well on drill bushings, taps and dies, 
small punches and the like. 

SHRINKING AND ENLARGING WORK 
Steel can be shrunk or enlarged by proper heating and cooling. 
Pins for forced fits can be enlarged several thousandths of an 
inch by careful heating to a dull red and quenching in water. 
The theory is that the metal is expanded in heating and that the 
sudden cooling sets the outer portion before the core can contract. 
In dipping the piece is not held under water till cold but is 
dipped, held a moment and removed. Then dipped again and 
again until cold. 

Rings and drawing dies are also shrunk in a similar way. 
The rings are heated to a cherry red, slipped on a rod or bolt 
and rolled in a shallow pan of water which cools only the outer 
edge. This holds the outside while the inner heated portion is 
forced inward, reducing the hole. This operation can be repeated 
a number of times with considerable success. 

TEMPERING ROUND DIES 

A number of circular dies of carbon tool steel for use in tool 
holders of turret lathes were required. No proper tempering 
oven was available, so the following method was adopted and 
proved quite successful; 

After the dies had been hardened dead hard in water, they 
were cleaned up bright. A pair of ordinary smiths' tongs was 
made with jaws of heavy material and to fit nicely all around 
the outside of the die, leaving a %2~ m - space when the jaws 
were closed around the die. The dies being all ready, the tongs 
were heated red hot, and the dies were picked up and held by 
the tongs. This tempered them from the outside in, left the 
teeth the temper required and the outside slightly softer. The 
dies held up the work successfully and were better than when 
tempered in the same bath. 

THE EFFECT OF TEMPERING ON WATER-QUENCHED GAGES 
The following information has been supplied by Automatic 

and Electric Furnaces, Ltd., 6, Queenstreet, London, S. W. : 
Two gages of % in. diameter, 12 threads per inch, were heated 

in a Wild-Barfield furnace, using the pyroscopic detector, and 



162 



THE WORKING OF STEEL 



were quenched in cold water. They were subsequently tempered 
in a salt bath at various increasing temperatures, the effective 
diameter of each thread and the scleroscope hardness being 
measured at each stage. The figures are in 10,000ths of an inch, 
and indicate the change + or — with reference to the original 

Table 24. — Changes Due to Quenching 



Thread 


After 
quenching 


Tempering temperature, degrees Centi 


grade 


220 


260 


300 


340 


380 


420 


1 


+25 


+ 19 


+ 17 


+ 15 


+ 13 


+ 11 


+ 11 


2 


+ 18 


+ 12 


+ 11 


+ 9 


+ 6 


+ 5 


+ 5 


3 


+ 12 


+ 6 


+ 5 


+ 3 











4 


+ 10 


+ 4 


+ 4 


+ 2 







- 1 


5 


+ 9 


+ 4 


+ 4 


+ 2 





o 





6 


+ 9 


+ 4 


+ 3 


+ 2 











7 


+ 10 


+ 5 


+ 5 


+ 3 


+ 2 


+ 1 


+ 2 


8 


+ 8 


+ 4 


+ 3 


+ 2 








+ 1 


9 


+ 9 


+ 4 


+ 3 


+ 2 


+ 1 


+ 1 


+ 1 


10 


+ 9 


+ 5 


+ 5 


+ 3 


+ 2 


+ 2 


+ 2 


11 


+ 7 


+ 4 


+ 4 


+ 2 


+ 1 


+ 1 


+ 1 


12 


+ 9 


+ 5 


+ 5 


+ 5 


+ 4 


+ 4 


+ 3 


Scleroscope 


80 


70 


70 


62 


56 


53 


52 



effective diameter of the gages. The results for the two gages 
have been averaged. 

Had these gages been formed with a plain cylindrical end 
projecting in front of the screw, the first two threads would 
have been prevented from increasing more than the rest. The 
gages would then have been fairly easily corrected by lapping 
after tempering at 220°C. Practically no lapping would be 
required if they were tempered at 340°C. There seems to be no 
advantage in going to a higher temperature than this. The 
same degree of hardness could have been obtained with consider- 
ably less distortion by quenching directly in fused salt. It is 
interesting to note that when the swelling after water quenching 
does not exceed 0.0012 in., practically the whole of it may be 
recovered by tempering at a sufficiently high temperature, 
but when the swelling exceeds this amount the steel assumes a 
permanently strained condition, and at the most only 0.0014 in. 
can be recovered by tempering. 



HARDENING CARBON STEEL FOR TOOLS 



163 



TEMPERING COLORS ON CARBON STEELS 

Opinions differ as to the temperature which is indicated by 
the various colors, or oxides, which appear on steel in tempering. 

The figures shown are from five different sources and while 
the variations are not great, it is safer to take the average tem- 
perature shown in the last column. 

Table 25. — Colors, Temperatures, Degrees Fahrenheit 



A B 


C D 

1 


E 


Average 


Faint yellow 


430 


430 


430 


430 


430 


430 


Light straw 


475 


460 


450 




450 


458 


Dark straw 


500 
525 


500 

530 


470 
520 


450 
530 


470 
510 


478 


Purple (reddis 


b). ...... 


523 


Purple (bluish) 




555 


550 


550 


550 


551 


Blue 




575 


585 
600 


560 


580 
600 


560 
610 


572 


Gray blue .... 




603 


Greenish blue 






625 




630 


627 








Table 26. — Another Color Table 


Degrees 
Fahrenheit 


High temperatures judged by color 


430 


Very pale yellow 








460 


Straw-yellow 








480 


Dark yellow 








500 
520 


Brown-yellow 
Brown-purple 


> Visible in full daylighl 






540 


Full purple 








560 


Full blue 








600 


Very dark blue 








752 


Red heat, visible in the dark 






885 


Red heat, visible in the twilight 






975 


Red heat, visible in the daylight 






1,292 


Dark red 






1,652 


Cherry-red 






1,832 


Bright cherry-red 






2,012 


Orange-red 






2,192 


Orange-yellow 






2,372 


Yellow-white 






2,552 


White welding heat 






2,732 


Brilliant white 






2,912 


Dazzling white (bluish-white) 







164 



THE WORKING OF STEEL 



These differences might easily be due to the difference in the 
light at the time the colors were observed. It must also be 
remembered that even a thin coating of oil will make quite a 
difference and cause confusion. It is these possible sources of 
error, coupled with the ever present chance of human error, 
that makes it advisable to draw the temper of tools in an oil 
bath heated to the proper temperature as shown by an accurate 
high-temperature thermometer. 

Another table, by Gilbert and Barker, runs to much higher tem- 
peratures. Beyond 2,200°, however, the eye is very uncertain. 

Table 26. — Colors for Tempering Tools 



Approximate 

color and 
temperature 



Kind of tool 



Yellow 
430 to 450°F. 



Thread chasers, hollow mills (solid type) twist drills, 
centering tools, forming tools, cut-off tools, profile cut- 
ters, milling cutters, reamers, dies, etc. 



Straw-yellow 
460°F. 



Thread rolling dies, counterbores, countersinks, shear 
blades, boring tools, engraving tools, etc. 



Brown-yellow 
500°F. 



Taps, Thread dies, cutters, reamers, etc. 



Light purple 
530°F. 



Taps, dies, rock drills, knives, punches, gages, etc. 



Dark purple 
550°F. 



Circular saws for metal, augers, dental and surgical in- 
struments, cold chisels, axes. 



Pale blue 
580°F. 



Bone saws, chisels, needles, cutters, etc. 



Blue 
600°F. 



Hack saws, wood saws, springs, etc. 



CHAPTER X 
HIGH-SPEED STEEL 

For centuries the secret art of making tool steel was handed 
down from father to son. The manufacture of tool steel is still 
an art which, by the aid of science, has lost much of its secrecy; 
yet tool steel is today made by practical men skilled as melters, 
hammer-men, and rollers, each knowing his art. These prac- 
tical men willingly accept guidance from the chemist and 
metallurgists. 

A knowledge of conditions existing today in the manufacture 
of high-speed steel is essential to steel treaters. It is well for 
the manufacturer to have steel treaters understand some of his 
troubles and difficulties, so that they will better comprehend 
the necessity of certain trade customs and practices, and, realiz- 
ing the manufacturer's desire to cooperate with them, will 
reciprocate. 

The manufacturer of high-speed steel knows and appreciates 
the troubles and difficulties that may sometimes arise in the 
heat-treating of his product. His aim is to make a uniform steel 
that will best meet the requirements of the average machine 
shop on general work, and at the same time allow the widest 
variation in heat treatment to give desired results. 

High speed steel is one of the most complex alloys known. A 
representative steel contains approximately 24 per cent of alloy- 
ing metals, namely, tungsten, chromium, vanadium, silicon, 
manganese, and in addition there is often found cobalt, molyb- 
denum, uranium, nickel, tin, copper and arsenic. 

STANDARD ANALYSIS 

The selection of a standard analysis by the manufacturer 
is the result of a series of compromises between various proper- 
ties imparted to the steel by the addition of different elements 
and there is a wide range of chemical analyses of various brands. 
The steel, to be within the range of generally accepted analysis, 
should contain over 16 per cent and under 20 per cent tungsten; 

165 



166 THE WORKING OF STEEL 

if of lower tungsten content it should carry proportionately more 
chromium and vanadium. 

The combined action of tungsten and chromium in steel gives 
to it the remarkable property of maintaining its cutting edge at 
relatively high temperature. This property is commonly spoken 
of as "red-hardness." The percentages of tungsten and chro- 
mium present should bear a definite relationship to each other. 
Chromiumim parts to steel a hardening property similar to that 
given by carbon, although to less a degree. The hardness im- 
parted to steel by chromium is accompanied by brittleness. 
The chromium content should be between 3.5 and 5 per cent. 

Vanadium was first introduced in high-speed steel as a "scaven- 
ger," thereby producing a more homogeneous product, of greater 
density and physical strength. It soon became evident that 
vanadium used in larger quantities than necessary as a scavenger 
imparted to the steel a much greater cutting efficiency. Recently, 
no less an authority than Prof. J. 0. Arnold, of the University 
of Sheffield, England, stated that "high-speed steels containing 
vanadium have a mean efficiency of 108.9, as against a mean 
efficiency of 61.9 obtained from those without vanadium content." 
A wide range of vanadium content in steel, from 0.5 to 1.5 per 
cent, is permissible. 

An ideal analysis for high-speed steel containing 18 per cent 
tungsten is a chromium content of approximately 3.85 per cent; 
vanadium, 0.85 to 1.10 per cent, and carbon, between 0.62 and 
0.77 per cent. 

Detrimental Elements. — Sulphur and phosphorus are two 
elements known to be detrimental to all steels. Sulphur causes 
"red-shortness" and phosphorus causes "cold-shortness." The 
detrimental effects of these two elements counteract each other 
to some extent but the content should be not over 0.02 sulphur 
and 0.025 phosphorus. The serious detrimental effect of small 
quantities of sulphur and phosphorus is due to their not being 
uniformly distributed, owing to their tendency to segregate. 

The manganese and silicon contents are relatively unimportant 
in the percentages usually found in high-speed steel. 

The detrimental effects of tin, copper and arsenic are not 
generally realized by the trade. Small quantities of these 
impurities are exceedingly harmful. These elements are very 
seldom determined in customers' chemical laboratories and it is 
somewhat difficult for public chemists to analyze for them. 



HARDENING CARBON STEEL FOR TOOLS 167 

In justice to the manufacturer, attention should be called to 
the variations in chemical analyses among the best of laboratories. 
Generally speaking, a steel works' laboratory will obtain results 
more nearly true and accurate than is possible with a customer's 
laboratory, or by a public chemist. This can reasonably be 
expected, for the steel works' chemist is a specialist, analyzing 
the same material for the same elements day in and day out. 

The importance of the chemical laboratory to a tool-steel 
plant cannot be over-estimated. Every heat of steel is analyzed 
for each element, and check analyses obtained; also, every 
substance used in the mix is analyzed for all impurities. The 
importance of using pure base materials is known to all manu- 
facturers despite chemical evidence that certain detrimental 
elements are removed in the process of manufacture. 

The manufacture of high-speed steel represents the highest 
art in the making of steel by tool-steel practice. Some may say, 
on account of our increased knowledge of chemistry and metal- 
lurgy, that the making of such steel has ceased to be an art, 
but has become a science. It is, in fact an art; aided by science. 
The human element in its manufacture is a decided factor, as 
will be brought in the following remarks: 

The heat treatment of steel in its broad aspect may be said 
to commence with the melting furnace and end with the harden- 
ing and tempering of the finished product. High-speed steel 
is melted by two general types of furnace, known as crucible 
and electric. Steel treaters, however, are more vitally interested 
in the changes that take place in the steel during the various 
processes of manufacture rather than a detailed description of 
those processes, which are more or less familiar to all. 

In order that good high-speed steel may be furnished in finished 
bars, it must be of correct chemical analysis, properly melted and 
cast into solid ingots, free from blow-holes and surface defects. 
Sudden changes of temperature are to be guarded against at 
every stage of its manufacture and subsequent treatment. The 
ingots are relatively weak, and the tendency to crack due to 
cooling strains is great. For this reason the hot ingots are not 
allowed to cool quickly, but are placed in furnaces which are of 
about the same temperature and are allowed to cool gradually 
before being placed in stock. Good steel can be made only from 
good ingots. 

Steel treaters should be more vitally interested in the impor- 



168 THE WORKING OF STEEL 

tant changes which take place in high-speed steel during the 
hammering operations than that of any other working the steel 
receives in the course of its manufacture. 

QUALITY AND STRUCTURE 

The quality of high-speed steel is dependent to a very great 
extent upon its structure. The making of the structure begins 
under the hammer, and the beneficial effects produced in this 
stage persist through the subsequent operations, provided they 
are properly carried out. The massive carbides and tungstides 
present in the ingot are broken down and uniformily distributed 
throughout the billet. 

To accomplish this the reduction in area must be sufficient and 
the hammer blows should be heavy, so as to carry the compres- 
sion into the center of the billet; otherwise, undesirable character- 
istics such as coarse structure and carbide envelopes will exist 
and cause the steel treater much trouble. Surface defects 
invisible in the ingot may be opened up under the hammering 
operation, in which event they are chipped from the hot billet. 

Ingots are first hammered into billets. These billets are 
carefully inspected and all surface defects ground or chipped. 
The hammered billets are again slowly heated and receive a 
second hammering, known as "cogging." The billet resulting 
therefrom is known as a " cogged" billet and is of the proper 
size for the rolling mill or for the finishing hammer. 

Although it is not considered good mill practice, some manu- 
facturers who have a large rolling mill perform the very impor- 
tant cogging operation in the rolling mill instead of under the 
hammer. Cogging in a rolling mill does not break up and dis- 
tribute the carbides and tungstides as efficiently as cogging 
under the hammer; another objection to cogging in the rolling 
mill is that there is no opportunity to chip surface defects de- 
veloped as they can be under the trained eye of a hammer-man, 
thereby eliminating such defects in the finished billet. 

The rolling of high-speed steel is an art known to very few. 
The various factors governing the proper rolling are so numerous 
that it is necessary for each individual rolling mill to work out 
a practice that gives the best results upon the particular analysis 
of steel it makes. Important elements entering into the rolling 



HARDENING CARBON STEEL FOR TOOLS 169 

are the heating and finishing temperatures, draft, and speed of 
the mill. In all of these the element of time must be considered. 

High-speed steel should be delivered from the rolling mill to the 
annealing department free from scale, for scale promotes the 
formation of a decarbonized surface. In preparation of bars 
for annealing, they are packed in tubes with a mixture of charcoal, 
lime, and other material. : The tubes are sealed and placed in the 
annealing furnace and the temperature is gradually raised to 
about 1,650°F., and held there for a sufficient length of time, 
depending upon the size of the bars. After very slow cooling 
the bars are removed from the tubes. They should then show 
a Brinnell number of between 235 and 275. 

The inspection department ranks with the chemical and metal- 
lurgical departments in safeguarding the quality of the product. 
It inspects all finished material from the standpoint of surface 
defects, hardness, size and fracture. It rejects such steel as is 
judged not to meet the manufacturer's standard. The inspection 
and metallurgical departments work hand in hand, and if any 
department is not functioning properly it will soon become evi- 
dent to the inspectors, enabling the management to remedy the 
trouble. 

The successful manufacture of high-speed steel can only be 
obtained by those companies who have become specialists. 
The art and skill necessary in the successful working of such steel 
can be attained only by a man of natural ability in his chosen 
trade, and trained under the supervision of experts. To become 
an expert operator in any department of its manufacture, it is 
necessary that the operator work almost exclusively in the pro- 
duction of such steel. 

As to the heat treatment, it is customary for the manufacturer 
to recommend to the user a procedure that will give to his steel 
a high degree of cutting efficiency. The recommendations of 
the manufacturer should be conservative, embracing fairly wide 
limits, as the tendency of the user is to adhere very closely 
to the manufacturer's recommendations. Unless one of the 
manufacturer's expert service men has made a detailed study of 
the customer's problem, the manufacturer is not justified in 
laying down set rules, for if the customer does a little experiment- 
ing he can probably modify the practice so as to produce results 
that are particularly well adapted to his line of work. 

The purpose of heat-treating is to produce a tool that will 



170 THE WORKING OF STEEL 

cut so as to give maximum productive efficiency. This cutting 
efficiency depends upon the thermal stability of the complex 
hardenites existing in the hardened and tempered steel. The 
writer finds it extremely difficult to convey the meaning of the 
word "hardenite" to those that do not have a clear conception 
of the term. The complex hardenites in high-speed steel may 
be described as that form of solid solution which gives to it its 
cutting efficiency. The complex hardenites are produced by heat- 
ing the steel to a very high temperature, near the melting point, 
which throws into solution carbides and tungstides, provided 
they have been properly broken up in the hammering process 
and uniformly distributed throughout the steel. By quenching 
the steel at correct temperature this solid solution is retained 
at atmospheric temperature. 

It is not the intention to make any definite recommendations 
as to heat-treating of high-speed steel by the users. It is recog- 
nized that such steel can be heat-treated to give satisfactory 
results by different methods. It is, however, believed that the 
American practice of hardening and tempering is becoming more 
uniform. This is due largely to the exchange of opinions in 
meetings and elsewhere. The trend of American practice for 
hardening is toward the following: 

First, slowly and carefully preheat the tool to a temperature 
of approximately 1,500°F., taking care to prevent the formation 
of excessive scale. 

Second, transfer to a furnace, the temperature of which is 
approximately 2,250 to 2,400°F., and allow to remain in the 
furnace until the tool is heated uniformly to the above 
temperature. 

Third, cool rapidly in oil, dry air blast, or lead bath. 

Fourth, draw back to a temperature to meet the physical 
requirements of the tool, and allow to cool in air. 

It was not very long ago that the desirability of drawing 
hardened high-speed steel to a temperature of 1,100° was pointed 
out, and it is indeed encouraging to learn that comparatively 
few treaters have failed to make use of this fact. Many treaters 
at first contended that the steel would be soft after drawing to 
this temperature and it is only recently, since numerous actual 
tests have demonstrated its value, that the old prejudice has 
been eliminated. 

High-speed steel should be delivered only in the annealed 



HARDENING CARBON STEEL FOR TOOLS 171 

condition because annealing relieves the internal strains inevi- 
table in the manufacture and puts it in vastly improved physical 
condition. The manufacturer's inspection after annealing also 
discloses defects not visible in the unannealed state. 

The only true test for a brand of high-speed steel is the service 
that it gives by continued performance month in and month 
out under actual shop conditions. The average buyer is not 
justified in conducting a test, but can well continue to purchase 
his requirements from a reputable manufacturer of a brand 
that is nationally known. The manufacturer is always willing 
to cooperate with the trade in the conducting of a test and is 
much interested in the information received from a well con- 
ducted test. A test, to be valuable, should be conducted in a 
manner as nearly approaching actual working conditions in the 
plant in which the test is made as is practical. In conducting a 
test a few reputable brands should be allowed to enter. All 
tools entered should be of exactly the same size and shape. 
There is much difference of opinion as to the best practical 
method of conducting a test, and the decision as to how the test 
should be conducted should be left to the customer, who should 
cooperate with the manufacturers in devising a test which would 
give the best basis for conclusions as to how the particular brands 
would perform under actual shop conditions. 

The value of the file test depends upon the quality of the file 
and the intelligence and experience of the person using it. The 
file test is not reliable, but in the hands of an experienced oper- 
ator, gives some valuable information. Almost every steel 
treater knows of numerous instances where a lathe tool which 
could be touched with a file has shown wonderful results as to 
cutting efficiency. 

Modern tool-steel practice has changed from that of the past, 
not by the use of labor-saving machinery, but by the use of 
scientific devices which aid and guide the skilled craftsman in 
producing a steel of higher quality and greater uniformity. 
It is upon the intelligence, experience, and skill of the individual 
that quality of tool steel depends. 

HARDENING HIGH-SPEED STEELS 

We will now take up the matter of hardening high-speed steels. 
The most ordinary tools used are for lathes and planers. The 



172 THE WORKING OF STEEL 

forging should be done at carbon-steel heat. Rough-grind while 
still hot and preheat to about carbon-steel hardening heat, then 
heat quickly in high-speed furnace to white heat, and quench in 
oil. If a very hard substance is to be cut, the point of tool may 
be quenched in kerosene or water and when nearly black, finish 
cooling in oil. Tempering must be done to suit the material to 
be cut. For cutting cast iron, brass castings, or hard steel, 
tempering should be done merely to take strains out of steel. 

On ordinary machinery steel or nickel steel the temper can be 
drawn to a dark blue or up to 900°F. If the tool is of a special 
form or character, the risk of melting or scaling the point cannot 
be taken. In these cases the tool should be packed, but if there is 
no packing equipment, a tool can be heated to as high heat as is 
safe without risk to cutting edges, and cyanide or prussiate of 
potash can be sprinkled over the face and then quenched in oil. 

Some very adverse criticism may be heard on this point, but 
experience has proved that such tools will stand up very nicely 
and be perfectly free from scales or pipes. Where packing can- 
not be done, milling cutters, and tools to be hardened all over, can 
be placed in muffled furnace, brought to 2,220° and quenched in 
oil. All such tools, however, must be preheated slowly to 1,400 
to 1,500° then placed in a high-speed furnace and brought up 
quickly. Do not soak high-speed steel at high heats. Quench in 
oil. 

We must bear in mind that the heating furnace is likely to 
expand tools, therefore provision must be made to leave extra 
stock to take care of such expansion. Tools with shanks such as 
counter bores, taps, reamers, drills, etc., should be heated no 
further than they are wanted hard, and quench in oil. If a 
forge is not at hand and heating must be done, use a muffle 
furnace and cover small shanks with a paste from fire clay or 
ground asbestos. Hollow mills, spring threading dies, and large 
cutting tools with small shanks should have the holes thoroughly 
packed or covered with asbestos cement as far as they are 
wanted soft. 

CUTTING-OFF STEEL FROM BAR 

To cut a piece from an annealed bar, cut off with a hack saw, 
milling cutter or circular saw. Cut clear through the bar ; do not 
nick or break. To cut a piece from an unannealed bar, cut right 
off with an abrasive saw; do not nick or break. If of large cross- 



HARDENING CARBON STEEL FOR TOOLS 173 

section, cut off hot with a chisel by first slowly and uniformly 
heating the bar, at the point to be cut, to a good lemon heat, 
1,800 to 1,850°F. and cut right off while hot; do not nick or 
break. Allow the tool length and bar to cool before reheating 
for forging. 

LATHE AND PLANER TOOLS 

Forging. — Gently warm the steel to remove any chill, is par- 
ticularly desirable in the winter, then heat slowly and carefully 
to a scaling heat, that is a lemon heat (1,800 to2,000°F.), and forge 
uniformly. Reheat the tool for further forging directly the steel 
begins to stiffen under the hammer. Under no circumstances 
forge the steel when the temperature falls below a dark lemon to 
an orange color about 1,700°F. Reheat as often as is necessary 
to finish forging the tool to shape. Allow the tool to cool after 
forging by burying the tool in dry ashes or lime. Do not place 
on the damp ground or in a draught of air. 

The heating for forging should be done preferably in a pipe or 
muffle furnace but if this is not convenient use a good clean fire 
with plenty of fuel between the blast pipe and the tool. Never 
allow the tool to soak after the desired forging heat has been 
reached. Do not heat the tool further back than is necessary 
to shape the tool, but give the tool sufficient heat. See that the 
back of the tool is flatly dressed to provide proper support under 
the nose of the tool. 

Hardening High-speed Steel. — Slowy reheat the cutting edge 
of the tool to a cherry red, 1,400°F., then force the blast so as to 
raise the temperature quickly to a full white heat, 2,200 to 
2,250°F., that is, until the tool starts to sweat at the cutting face. 
Cool the point of the tool in a dry air blast or preferably in oil,- 
further cool in oil keeping the tool moving until the tool has 
become black hot. 

To remove hardening strains reheat the tool to from 500 to 
1,10'0°F. Cool in oil or atmosphere. This second heat treat- 
ment adds to the toughness of the tool and therefore to its life. 

Grinding Tools. — Grind tools to remove all scale. Use a 
quick-cutting, dry, abrasive wheel. If using a wet wheel, be 
sure to use plenty of water. Do not under any circumstances 
force the tool against the wheel so as to draw the color, as this is 
likely to set up checks on the surface of the tool to its detriment. 



174 . THE WORKING OF STEEL 

FOR MILLING CUTTERS AND FORMED TOOLS 

Forging — Forge as before. — Annealing. — Place the steel in a 
pipe, box or muffle. Arrange the steel so as to allow at least 1 
in. of packing, consisting of dry powder ashes, powdered charcoal, 
mica, etc., between the pieces and the walls of the box or pipe. 
If using a pipe close the ends. Heat slowly and uniformly to a 
cherry red, 1,375 to 1,450°F. according to size. Hold the steel 
at this temperature until the heat has thoroughly saturated 
through the metal, then allow the muffle box and tools to cool 
very slowly in a dying furnace or remove the muffle with its 
charge and bury in hot ashes or lime. The slower the cooling 
the softer the steel. 

The heating requires from 2 to 10 hr. depending upon the size 
of the piece. 

Hardening and Tempering. — It is preferable to use two fur- 
naces when hardening milling cutters and special shape tools. 
One furnace should be maintained at a uniform temperature from 
1,375 to 1,450°F. while the other should be maintained at about 
2,250°F. Keep the tool to be hardened in the low temperature 
furnace until the tool has attained the full heat of this furnace. 
A short time should be allowed so as to be assured that the center 
of the tool is as hot as the outside. Then quickly remove the 
tool from this preheating furnace to the full heat furnace. Keep 
the tool in this furnace only as long as is necessary for the tool to 
attain the full temperature of this furnace. Then quickly remove 
and quench in oil or in a dry air blast. Remove before the tool 
is entirely cold and draw the temper in an oil bath by raising the 
temperature of the oil to from 500 to 750°F. and allow this tool 
to remain, at this temperature, in the bath for at least 30 min., 
•insuring uniformity of temper; then cool in the bath, atmosphere 
or oil. 

If higher drawing temperatures are desired than those possible 
with oil, a salt bath can be used. A very excellent bath is made 
by mixing two parts by weight of crude potassium nitrate and 
three parts crude sodium nitrate. These will melt at about 450°F. 
and can be used up to 1,000°F. Before heating the steel in 
the salt bath, slowly preheat, preferably in oil. Reheating the 
hardened high-speed steel to 1,000°F. will materially increase the 
life of lathe tools, but milling and form cutters, taps, dies, etc., 
should not be reheated higher than 500 to 650°F., unless extreme 



HARDENING CARBON STEEL FOR TOOLS 175 

hardness is required, when 1,100 to 1,000°F., will give the hardest 
edge. 

INSTRUCTIONS FOR WORKING HIGH-SPEED STEEL 

Owing to the wide variations in the composition of high-speed 
steels by various makers, it is always advisable to follow the 
directions of each when using his brand of steel. In the absence 
of specific directions the following general suggestions from 
several makers will be found helpful. 

The Ludlum Steel Company recommend the following : 
Cutting-off. — To cut a piece from an annealed bar, cut off 
with a hack saw, milling cutter or circular saw. Cut clear 
through the bar; do not nick or break. To cut a piece from 
an unannealed bar, cut right off with an abrasive saw; do not 
nick or break. If of large cross-section, cut off hot with a chisel 
by first slowly and uniformly heating the bar, at the point to 
be cut, to a good lemon heat, 1800°-1850°F. and cut right off 
while hot; do not nick or break. Allow the tool length and bar 
to cool before reheating for forging. 

LATHE AND PLANER TOOLS 

To Forge.— Gently w T arm the steel to remove any chill, is 
particularly desirable in the winter, then heat slowly and care- 
fully to a scaling heat, that is a lemon heat (1800°-2000°F.), and 
forge uniformly. Reheat the tool for further forging directly 
the steel begins to stiffen under the hammer. Under no cir- 
cumstances forge the steel when the temperature falls below a 
dark lemon to an orange color about 1700°F. Reheat as often 
as is necessary to finish forging the tool to shape. Allow the 
tool to cool after forging by burying the tool in dry ashes or 
lime. Do not place on the damp ground or in a draught of air. 

The heating for forging should be done preferably in a pipe 
or muffle furnace but if this is not convenient use a good clean 
fire with plenty of fuel between the blast pipe and the tool. 
Never allow the tool to soak after the desired forging heat has 
been reached. Do not heat the tool further back than is ne- 
cessary to shape the tool, but give the tool sufficient heat. 
See that the back of the tool is flatly dressed to provide proper 
support under the nose of the tool. 



176 THE WORKING OF STEEL 

Hardening. — Slowly reheat the cutting edge of the tool to a 
cherry red, 1400°F., then force the blast so as to raise the tem- 
perature quickly to a full white heat, 2200°-2250°F., that is, 
until the tool starts to sweat at the cutting face. Cool the 
point of the tool in a dry air blast or preferably in oil, further 
cool in oil keeping the tool moving until the tool has become 
black hot. 

To remove hardening strains reheat the tool to from 500° to 
1100°F. Cool in oil or atmosphere. This second heat treat- 
ment adds to the toughness of the tool and therefore to its life. 

Grinding. — Grind tools to remove all scale. Use a quick 
cutting, dry, abrasive wheel. If using a wet wheel, be sure to 
use plenty of water. Do not under any circumstances force 
the tool against the wheel so as to draw the color, as this is 
likely to set up checks on the surface of the tool to its detriment. 

The Firth-Sterling Steel Company say: 

Instead of printing any rules on the hardening and temper- 
ing of Firth-Sterling Steels we wish to say to our customers : 
Trust the steel to the skill and the judgement of your Tool- 
smith and Tool Temperer. 

The steel workers of today know by personal experience and by 
inheritance all the standard rules and theories on forging, hardening and 
tempering of all fine tool steels. They know the importance of slow, 
uniform heating, and the danger of overheating some steels, and under- 
heating others. 

The tempering of tools and dies is a science taught by heat, muscle 
and brains. 

The tool temperer is the man to hold responsible for results. The 
tempering of tools has been his life work. He may find suggestions on 
the following pages interesting, but we are always ready to trust the 
treatment of our steels to the experienced man at the fire. 

HEAT TREATMENT OF LATHE, PLANER AND SIMILAR TOOLS 

Fire. — For these tools a good fire is one made of hard foundry coke, 
broken in small pieces, in an ordinary blacksmith forge with a few bricks 
laid over the top to form a hollow fire. The bricks should be thor- 
oughly heated before tools are heated. Hard coal may be used very 
successfully in place of hard coke and will give a higher heat. It is 
very easy to give Blue Chip the proper heat if care is used in making up 
the fire. 

Forging. — Heat slowly and uniformly to a good forging heat. Do not 
hammer the steel after it cools below a bright red. Avoid as much as 



HARDENING CARBON STEEL FOR TOOLS 177 

possible heating the body of the tool, so as to retain the natural tough- 
ness in the neck of the tool. 

Hardening. — Heat the point of the tool to an extreme white heat 
(about 2,200°F.) until the flux runs. This heat should be the highest 
possible short of melting the point. Care should be taken to confine 
the heat as near to the point as possible so as to leave the annealing and 
consequent toughness in the neck of the tool and where the tool is held 
in the tool post. 

Cool in an air blast, the open air or in oil, depending upon the tools 
or the work thej' are to do. 

For roughing tools temper need not be drawn except for work where 
the edge tends to crumble on account of being too hard. 

For finishing tools draw the temper to suit the purpose for which 
they are to be used. 

Grind thoroughly on dry wheel (or wet wheel if care is used to pre- 
vent checking). 

HEAT TREATMENT OF MILLING CUTTERS, DRILLS, 
REAMERS, ETC. 

The Fire. — Gas and electric furnaces designed for high heats are now 
made for treating high-speed steels. We recommend them for treating 
all kinds of Blue Chip tools and particularly the above class. After 
tools reach a yellow heat in the forge fire they must not be allowed to 
touch the fuel or come in contact with the blast or surrounding air. 

Heating. — Tools of this kind should be heated to a mellow white heat, 
or as hot as possible without injuring the cutting edges (2,000 
to 2,200°F.). For most work the higher the heat the better the tool. 
Where furnaces are used, we recommend preheating the tools to a red 
heat in one furnace before putting them in a white hot furnace. 

Cooling. — We recommend quenching all of the above tools in oil 
when taken from the fire. We have found fish oil, cottonseed oil, 
Houghton's No. 2 soluble oil and linseed oil satisfactory. The high 
heat is the important thing in hardening Blue Chip tools. If a white hot 
tool is allowed to cool in the open air it will be hard, but the air scales the 
tool. 

Drawing the Temper. — Tools of this class should be drawn consider- 
ably more than water-hardening steel for the same purpose. 

HEAT TREATMENT OF PUNCHES AND DIES, SHEARS, 
TAPS, ETC. 

Heating. — The degree to which tools of the above classes should be 
heated depends upon the shape, size and use for which they are in- 
tended. Generally, they should not be heated to quite as high a heat 

12 



178 THE WORKING OF STEEL 

as lathe tools or milling cutters. They should have a high heat, 
but not enough to make the flux run on the steel (by pyrometer 1,900 
to 2,100°F.). 

Cooling. — Depending on the tools, some should be dipped in oil all 
over, some only part way, and others allowed to cool down in the air 
naturally, or under air blast. In cooling, the toughness is retained by 
allowing some parts to cool slowly and quenching parts that should be 
hard. 

Drawing the Temper. — As in cooling, some parts of these tools will 
require more drawing than others, but, on the whole, they must be 
drawn more than water hardening tools for the same purpose or to 
about 500°F. all over, so that a good file will just " touch" the cutting 
or working parts. 

Barium Chloride Process. — This is a process developed for treating 
certain classes of tools, such as taps, forming tools, etc. It is being 
successfully used in many large plants. Briefly the treatment is as 
follows : 

In this treatment the tools are first preheated to a red heat, but small 
tools may be immersed without preheating. The barium chloride bath 
is kept at a temperature of from 2,000 to 2,100°F., and tools are held 
in it long enough to reach the same temperature. They are then dipped 
in oil. The barium chloride which adheres to the tools is brushed off, 
leaving the tools as clean as before heating. 

A CHROMIUM-COBALT STEEL 

The Latrobe Steel Company make a high-speed steel without 
tungsten, its red-hardness properties depending on chromium 
and cobalt instead of tungsten. It is known as P. R. K-33 steel. 
It does not require the high temperature of the tungsten steels, 
hardening at 1,830 to 1,850°F. instead of 2,200° or even higher, 
as with the tungsten. 

This steel is forged at 1,900 to 2,000°F. and must not be 
worked at a lower temperature than 1,600°F. It requires 
soaking in the fire more than the tungsten steels. It can be 
normalized by heating slowly and thoroughly to 1,475°F., holding 
this for from 10 to 20 min. according to the size of the piece and 
cooling in the open air, protected from drafts. 

A peculiarity of this steel is that it becomes non-magnetic 
at or above 1,960°F. and the magnetic quality is not restored by 
cooling. Normalizing as above, however, restores the magnetic 
qualities. This enables the user to detect any tools which have 
been overheated, with a horseshoe magnet. 



HARDENING CARBON STEEL FOR TOOLS 179 

It is sometimes advantageous to dip tools, before heating for 
hardening, in ordinary fuel or quenching oil. The oil leaves a 
thin film of carbon which tends to prevent decarbonization, 
giving a very hard surface. 

For other makes of high-speed steel used in lathe and planer 
tools the makers recommend that the tools be cut from the bar 
with a hack saw or else heated and cut with a chisel. The 
heating should be very slow until the steel reaches a red after 
which it can be heated more rapidly and should only be forged 
at a high heat. It can be forged at very high heats but care 
should be taken not to forge at a low heat. The heating should 
be uniform and penetrate clear to the center of the bar before 
forging is begun. Reheat as often as necessary to forge at the 
proper heat. 

After forging cool in lime before attempting to harden. Do 
not attempt to harden with the forging heat as was sometimes 
done with the carbon tools. 

For hardening forged tools, heat slowly up to a bright red 
and then rapidly until the point of the tool is almost at a melting 
heat. Cool in a blast of cold, dry air. For large sizes of steel, 
cool in linseed oil or in fish oil as is most convenient. If the 
tools are to be used for finishing cuts heat to a bright yellow and 
quench in oil. Grind for use on a sand wheel or grindstone 
in preference to an emery or an artificial abrasive wheel. 

For hardening milling and similar cutters, preheat to a bright 
red, place the cutter on a round bar of suitable size, and revolve 
it quickly over a very hot fire. Heat as high as possible without 
melting the points of the teeth and cool in a cold blast of dry 
air or in fish oil. 

Light fragile cutters, twist drills, taps and formed cutters may 
be heated almost white and then dipped in fish oil for hardening. 
Where possible it is better to give an even higher heat and cool 
in the blast of cold, dry air as previously recommended. 

SUGGESTIONS FOR HANDLING HIGH-SPEED STEELS 

The following suggestions for. handling high-speed steels 
are given by a maker whose steel is probably typical of a number 
of different makes, so that they will be found useful in other 
cases as well. These include hints as to forging as well as 
hardening, together with a list of "dont's" which are often 



180 



THE WORKING OF STEEL 



very useful. This applies to forging, hardening of lathe, slot- 
ting, planing and all similar tools. 




Fig. 74. — All-steel, % in. square, J^ X 1 in., and larger is usually mild finished, 
and can be cut in a hack saw. If cut off hot, be sure to heat the butt end slowly 
and thoroughly in a clean fire. Rapid and insufficient heating invariably cracks 
the steel. If you want to stamp the end with the name of the steel, it is necessary 
that this is done at a good high orange color heat, as it is otherwise apt to split 
the steel. (Take your time, do not hurry.) 

Hardening High-speed Steel 

In forging use coke for fuel in the forge. Heat steel slowly and thoroughly 
to a lemon heat. Do not forge at a lower heat. Do not let the steel cool 




Fig. 75. — Be sure to have a full yellow heat at the dotted line. Remember 
this is a boring mill tool and will stand out in the tool-post, and if you do not 
have a high thorough lemon heat, your tool will snap off at the dotted line. 
(Ninety-five per cent of all tools which break, have been forged at too low a 
heat or at a heat not thorough to the center.) 

below a bright cherry red while forging. After the tool is dressed, reheat 
to forging heat to remove the forging strain, and lay on the floor until cold. 
Then have the tool rough ground on a dry emery wheel. 




Fig. 76. — Keep your high lemon forging heat up. If you forge under a steam 
hammer, take light blows. Do not jam your tool into shape. Put frequently 
back into the fire. Never let the high lemon color go down and beyond the 
dotted line. 

For built-up and bent tools special care should be taken that the forging 
heat does not go below a bright cherry. For tools % by 1% or larger where 



HARDENING CARBON STEEL FOR TOOLS 



181 



there is a big strain in forging, such as bending at angles of about 45 deg. 
and building the tools up, they should be heated to at least 1,700°F. slowly 
and without much blast. For a % by 1%, tool it should take about 10 min. 
with the correct blast in a coke fire. Larger tools in proportion. They can 




Fig. 77. — Be sure that the tool is absolutely straight at the bottom, so as to lie 
flat in the tool-post. 

then be bent readily, but no attempt should be made to forge the steel 
further without reheating to maintain the bright cherry red. This is essen- 
tial, as otherwise the tools crack in hardening or while in use. 




Fig. 78. — This is the finished forged tool, and let this grow cold by itself, 
the slower the better. It is well to cool the tool slowly in hot ashes, to remove 
all forging strain. You can now grind the tool dry on a sharp emery wheel. 
The more you now finish the tool in grinding, the less there is to come off after 
hardening. 

In hardening place the tool in a coke fire (hollow fire if possible) with a 
slow blast and heat gradually up to a white welding heat on the nose of the 
tool. Then dip the white hot part only into thin oil or hold in a strong 




Fig. 79. — This tool is ground, ready for hardening. 

forging heat. 



Never harden from the 



cold' air blast. When hardening in oil do not hold the tool in one place 
but keep it moving so that it cools as quickly as possible. It is not neces- 
sary to draw the temper after hardening these tools. 

In grinding all tools should be ground as lightly as possible on a soft wet 



182 



THE WORKING OF STEEL 




Fig. 80. — Heat the nose of the tool only up to dotted line, very slowly and 
thoroughly to an absolutely white welding heat, so that it shows a trifle fused 
around the edges, and be very sure that this fusing has gone thoroughly through 
the nose, otherwise the fusing effect will be taken off after the second grinding. 
Note the difference of the nose between this and Fig. 79. 




Fig. 81. — Shows unnecessary roasting and drossing. Such hardening requires 
a great amount of grinding and is not good. After hardening grind carefully 
on a wet emery wheel, and be sure that the wheel is sharp with a plentiful supply 
of water. Do not force the grinding, otherwise the cold water striking the steel 
heated up by friction, will crack the nose. Be sure that the grinding wheel is 
sharp. | 



HARDENING CARBON STEEL FOR TOOLS 183' 

sandstone or on a wet emery wheel, and care should be taken not to create 
any surface cracks, which are invariably the result of grinding too forcibly. 
The following illustrations, Figs. 74 to 81, with their captions, will be 
found helpful. 

Special points of caution to be observed when hardening high-speed 
steel. 

Don't use a green coal fire; use coke, or build a hollow fire. 

Don't have the bed of the fire free from coal. 

Don't hurry the heating for forging. The heating has to be done very 
slowly and the forging heat has to be kept very high (a full lemon color) 
heat and the tool has to be continually brought back into the fire to keep the 
high heat up. When customers complain about seams and cracks, in 9 
cases out of 10, this has been caused by too low a forging heat, and when 
the blacksmith complains about tools cracking, it is necessary to read 
this paragraph to him. 

Don't try to jam the tool into shape under a steam hammer with one or 
two blows; take easy blows and keep the heat high. 

Don't have the tool curved at the bottom; it must lie perfectly flat in 
the tool post. 

Don*t harden from your forging heat; let the tool grow cold or fairly cold. 

After forging you can rough grind the tool dry, but not too forcibly. 

Don't, for hardening, get more than the nose white hot. 

Don't get the white heat on the surface only. 

Don't hurry your heating for hardening; let the heat soak thoroughly 
through the nose of the tool. 

Don't melt the nose of the tool. 

Don't, as a rule, dip the nose into water; this should be done only for 
extremely hard material. It is dangerous to put the nose into water for 
fear of cracking and when you do put the nose into water put just J^ in. 
only of the extreme white hot part into the water and don't keep it too long 
in the water; just a few seconds, and then harben in oil. We do not recom- 
mend water hardening. 

Don't grind too forcibly. 

Don't grind dry after hardening. 

Don't discolor the steel in grinding. 

Don't give too much clearance on tools for cutting cast iron. 

Don't start on cast iron with a razor edge on the tool. Take an oil stone 
and wipe three or four times over the razor edge. 

Don't use tool holder steel from bars without hardening the nose of each 
individual tool bit. 

Air-hardening Steels. — These steels are recommended for 
boring, turning and planing where the cost of high-speed seems 
excessive. They are also recommended for hard wood knives, 
for roughing and finishing bronze and brass, and for hot bolt 
forging dies. This steel cannot be cut or punched cold but can 
be shaped and ground on abrasive wheels of various kinds. 

It should be heated slowly and evenly for forging and kept 



184 THE WORKING OF STEEL 

as evenly heated at a bright red as possible. It should not be 
forged after it cools to a dark red. 

After the tool is made, heat it again to a bright red and lay 
it down to cool in a dry place or it can be cooled in a cold, dry 
air blast. Water must be kept away from it while it is hot. 



CHAPTER XI 
FURNACES 

There are so many standard furnaces now on the market that 
it is not necessary to go into details of their design and construc- 





Fig. 82. — Standard lead pot furnace. 

tion and only a few will be illustrated. Oil, gas and coal or 
coke are most common but there is a steady growth of the use of 
electric furnaces. 

185 



186 



THE WORKING OF STEEL 



Typical Oil-fired Furnaces. — Several types of standard oil- 
fired furnaces are shown herewith. Figure 82 is a lead pot 
furnace, Fig. 83 is a vertical furnace with a center column. 
This column reduces the cubical contents to be heated and also 
supports the cover. 





Fig. 83.— Furnace with center column. 

A small tool furnace is shown in Fig. 84 which gives the con- 
struction and heat circulation. A larger furnace for high-speed 
steel is given in Fig. 85. The steel is supported above the heat, 
the lower flame passing beneath the support. 

For hardening broaches and long reamers and tops, the furnace 
shown in Fig. 86 is used. Twelve jets are used, these coming in 
radially to produce a whirling motion. 



FURNACES 



187 



Oil and gas furnaces may be divided into three types : the open 
heating chamber in which combustion takes place in the chamber 
and directly over the stock; the semimume heating chamber in 




B-<=£ =n 



Fig. 84. — Furnace for cutting tools. 



which combustion takes place beneath the floor of the chamber 
from which the hot gases pass into the chamber through suit- 







Fig. 85. — High-speed steel furnace. 

able openings; and the muffle heating chamber in which the heat 
entirely surrounds the chamber but does not enter it. The 
open furnace is used for forging, tool dressing and welding. The 
muffle furnace is used for hardening dies, taps, cutters and similar 



188 



THE WORKING OF STEEL 



tools of either carbon or high-speed steel. The muffle furnace is 
for spring hardening, enameling, assaying and work where the 
gases of combustion may have an injurious effect on the material. 




j" 



r 



H 3"* 



:•: ■■■ 

■'■-: 



I 

■■!; 
J.LJ 



" 



2f 



3 Y 



3 



3T 






ft 



FT 



; ■; ^ 






*%A 



z 



V 



Fig. 86. — Furn'ace for hardening broaches. 



Furnaces of these types of oil-burning furnaces are shown in 
Figs. 87, 88 and 89; these being made by the Gilbert & Barker 
Manufacturing Company. The first has an air curtain formed 



FURNACES 



189 




,i" fW ,: : v,,,,, ; . : t>- 



msm 




' :< 







^Hy 



190 



THE WORKING OF STEEL 



by jets from the large pipe just below the opening, to protect the 
operator from heat. 




Fig. 90. — Gas fired furnace. 

oft 




SECTIONAL FLAN 




LONGITUDtNAL SECTION 



CROSS SECTION 



Fig. 91. — Car door type of annealing furnace. 

Oil furnaces are also made for both high- and low-pressure air, 
each having its advocates. The same people also make gas- 
fired furnaces. 

Several types of furnaces for various purposes are illustrated 



FURNACES 191 

in Figs. 90 and 91. The first is a gas-fired hardening furnace of 
the surface-combustion type. 

A large gas-fired annealing furnace of the Maxon system is 
shown in Fig. 91. This is large enough for a flat car to be run 
into as can be seen. It shows the arrangement of the burners, 
the track for the car and the way in which it fits into the furnace. 
These are from the designs of the Industrial Furnace Corporation. 

Before deciding upon the use of gas or oil, all sides of the 
problem should be considered. Gas is perhaps the nearest ideal 
but is as a rule more expensive. The tables compiled by the 
Gilbert & Barker Manufacturing Company and shown herewith, 
may help in deciding the question. 

Table 27. — Showing Comparison of Oil Fuel with Various Gaseous 

Fuels 

Heat units 

per thousand 

cubic feet 

Natural gas 1,000,000 

Air gas (gas machine) 20 cp 815,500 

Public illuminating gas, average 650,000 

Water gas (from bituminous coal) •>.... 377,000 

Water and producer gas, mixed 175,000 

Producer gas 150,000 

Since a gallon of fuel oil (7 lb.) contains 133,000 heat units, the following 
comparisons may evidently be made. At 5 cts. a gallon, the equivalent 
heat units in oil would equal: 

Per thousand 
cubic feet 

Natural gas at $0,375 

Air gas, 20 cp at 0.307 

Public illuminating gas, average at . 244 

Water gas (from bituminous coal) at . 142 

Water and producer gas, mixed at . 065 

Producer gas at . 057 

Comparing oil and coal is not always simple as it depends on the 
work to be done and the construction of the furnaces. The 
variation rises from 75 to 200 gal. of oil to a ton of coal. For 
forging and similar work it is probably safe to consider 100 gal. 
of oil as equivalent to a ton of coal. 

Then there is the saving of labor in handling both coal and 
ashes, the waiting for fires to come up, the banking of fires and 
the dirt and nuisance generally. The continuous operation 
possible with oil adds to the output. 



192 THE WORKING OF STEEL 

When comparing oil and gas it is generally considered that 4^ 
gal. of fuel oil will give heat equivalent to 1,000 cu. ft. of coal gas. 

The pressure of oil and air used varies with the system in- 
stalled. The low-pressure system maintains a pressure of about 
8 oz. on the oil and draws in free air for combustion. Others use 
a pressure of several pounds, while gas burners use an average of 
perhaps 1^ lb. of air to give best results. 

The weights and volumes of solid fuels are: Anthracite coal, 
55 to 65 lb. per cubic feet or 34 to 41 cubic feet per ton; bitu- 
minous coal, 50 to 55 lb. per cubic feet or 41 to 45 cubic feet per 
ton; coke, 28 lb. per cubic feet or 80 cubic feet per ton — the ton 
being calculated as 2,240 lb. in each case. 

A novel carburizing furnace that is being used by a number of people, is 
built after the plan of a tireless cooker. The walls of the furnace are extra 
heavy, and the ports and flues are so arranged that when the load in the 
furnace and the furnace is thoroughly heated, the burners are shut off and 
all openings are tightly sealed. The carburization then goes on for several 
hours before the furnace is cooled below the effective carburizing range, 
securing an ideal diffusion of carbon between the case and the core of the 
steel being carburized. This is particularly adaptable where simple steel 
is used. 

PROTECTIVE SCREENS FOR FURNACES 

Workmen needlessly exposed to the flames, heat and glare 
from furnaces where high temperatures are maintained suffer in 
health as well as in bodily discomfort. This shows several types 
of shields designed for the maximum protection of the furnace 
worker. 

Bad conditions are not necessary; in almost every case means 
of relief can be found by one earnestly seeking them. The larger 
forge shops have adopted flame shields for the majority of their 
furnaces. Years ago the industrial furnaces (particularly of the 
oil-burning variety) were without shields, but the later models 
are all shield-equipped. These shields are adapted to all of the 
more modern, heat-treating furnaces, as well as to those fur- 
naces in use for working forges; and attention should be paid to 
their use on the former type since the heat-treating furnaces are 
constantly becoming more numerous as manufacturers find need 
of them in the many phases of munitions making or similar work. 

The heat that the worker about these furnaces must face may 
be divided in general into two classes : there is first that heat due 
to the flame and hot gases that the blast in the furnaces forces 



FURNACES 193 

out onto a man's body and face. In the majority of furnaces 
this is by far the most discomforting, and care must be taken to 
fend it and turn it behind a suitable shield. The second class is 
the radiant heat, discharged as light from the glowing interior of 
the furnace. This is the lesser of the two evils so far as general 
forging furnaces are concerned, but it becomes the predominating 
feature in furnaces of large door area such as in the usual case- 
hardening furnaces. Here the amount of heat discharged is 
often almost unbearable even for a moment. This heat can be 
taken care of by interposing suitable, opaque shields that will 
temporarily absorb it without being destroyed by it, or becoming 
incandescent. Should such shields be so constructed as to close 
off all of the heat, it might be impossible to work around the 
furnace for the removal of its contents, but they can be made 
movable, and in such a manner as to shield the major portion of 
the worker's body. 

First taking up the question of flame shields, the illustration, 
Fig. 92, is a typical installation that shows the main features for 
application to a forging machine or drop-hammer, oil-burning 
furnace, or for an arched-over, coal furnace where the flame blows 
out the front. This shield consists of a frame covered with sheet 
metal and held by brackets about 6 in. in front of the furnace. 
It will be noted that slotted holes make this frame adjustable 
for height, and it should be lowered as far as possible when in use, 
so that the work may just pass under it and into the furnace 
openings. 

Immediately below the furnace openings, and close to the 
furnace frame will be noted a blast pipe carrying air from the 
forge-shop fan. This has a row of small holes drilled in its 
upper side for the entire length, and these direct a curtain of 
cold air vertically across the furnace openings, forcing all of the 
flame, or a greater portion of it, to rise behind the shield. Since 
the shield extends above the furnace top there is no escape for 
this flame until it has passed high enough to be of no further 
discomfort to the workman. 

In this case fan-blast air is used for cooling, and this is cheaper 
and more satisfactory because a great volume may be used. 
However, where high-pressure air is used for atomizing the oil at 
the burner, and nothing else is available, this may be employed — 
though naturally a comparatively small pipe will be needed, in 
which minute holes are drilled, else the volume of air used will 

13 



194 



THE WORKING OF STEEL 




FURNACES 195 

be too great for the compressor economically to supply. Steam 
may also be employed for like service. 

The latest shields of this type are all made double, as illus- 
trated, with an inner sheet of metal an inch or two inside of the 
front. In the illustration, A, Fig. 92, this inner sheet is smaller, 
but some are now built the same size as the front and bolted to 
it with pipe spacers between. The advantage of the double 
sheet is that the inner one bears the brunt of the flame, and, if 
needs be, burns up before the outer; while, if due to a heavy 
fire it should be heated red at any point, the outer sheet will 
still be much cooler and act as an additional shield to the furnace 
man. 

Heavy Forging Practice.— In heavy forging practice where the 
metal is being worked at a welding heat, the amount of flame that 
will issue from an open-front furnace is so great that a plain, 
sheet-steel front will neither afford sufficient protection nor 
stand up in service. For such a place a water-cooled front is 
often used. The general type of this front is illustrated in Fig. 93, 
and appears to have found considerable favor, for numbers of 
its kind are scattered throughout the country. 

In this case the shield is placed at a slight angle from the 
vertical, and along the top edge is a water pipe with a row of 
small holes through which sprays of water are thrown against it. 
This water runs down in a thin sheet over the shield, cooling it, 
and is collected in a trough connected with a run-off pipe at the 
bottom. The lower blast-pipe arrangement is similar to the one 
first described. 

There are several serious objections to this form of shield that 
should lead to its replacement by a better type; the first is that 
with a very hot fire, portions in the center may become so rapidly 
heated that the steam generated will part the sheet of water and 
cause it to flow from that point in an inverted V, and that section 
will then quickly become red hot. Another feature is that after 
the water and fire are shut down for the night the heat of the 
furnace can be great enough to cause serious warping of the 
surface of the shield so that the water will no longer cover it in a 
thin, uniform sheet. 

After rigging up a big furnace with a shield of this type several 
years ago, its most serious object was found in the increase of the 
water bill of the plant. This was already of large proportions, 
but it had suddenly jumped to the extent of several hundred 



196 THE WORKING OF STEEL 

dollars. Investigation soon disclosed the fact that this water 
shield was one of the main causes of the added cost of water. A 
little estimating of the amount of water that can flow through a 
l^-in. pipe under 30-lb. pressure, in the course of a day, will 
show that this amount at 10 cts. per 1,000 gal., can count up 
rather rapidly. 

Figure 93 is a section through a portion of the furnace front 
and shield showing all of the principal parts. This shield consists 
essentially of a very thin tank, about 2}^ in. between walls, and 
filled with water. Like other shields it is fitted with an adjust- 
ment, that it may be raised and lowered as the work demands. 
The tank having an open top, the water as it absorbs heat from 
the flame will simply boil away in steam ; and only a small amount 
will have to be added to make up for that which has evaporated. 
The water-feed pipe shown at F ends a short distance above the 
top of the tank so that just how much water is running in may 
readily be seen. 

An overflow pipe is provided at which aids in maintaining 
the water at the proper height, as a sufficient quantity can al- 
ways be permitted to run in, to avoid any possibility of the shield 
ever boiling dry; at the same time the small excess can run off 
without danger of an overflow. The shield illustrated in Fig. 94 
has been in constant use for over two years, giving greater 
satisfaction than any other of which the writer has known. It 
might also be noted that this shield was made with riveted 
joints, the shop not having a gas-welding outfit. To flange over 
the edges and then weld them with an acetylene torch would be 
a far more economical procedure, and would also insure a tight 
and permanent joint. 

The water-cooled front shown in Fig. 95 is an absurd effort to 
accomplish the design of a furnace that will provide cool working 
conditions. This front was on a bolt-heating furnace using hard 
coal for fuel; and it may be seen that it takes the place of all of 
the brickwork that should be on that side. Had this been noth- 
ing more than a very narrow water-cooled frame, with brickwork 
below and supporting bricks above, put in like the tuyeres in a 
foundry cupola, the case would have been somewhat different, 
for then it would have absorbed a smaller proportion of the heat. 

A blacksmith who knows how a piece of cold iron laid in a 
small welding furnace momentarily lowers the temperature, 
will appreciate the enormous amount of extra heat that must 
be maintained in the central portion of this furnace to make up 



FURNACES 197 

for the constant chilling effect of the cold wall. Moreover, since 
there would have been serious trouble had steam generated in 
this front, a steady stream of water had to be run through it 
constantly to insure against an approach to the boiling point, 
This is illustrated because of its absurdity, and as a warning of 
something to avoid. 

Water-cooled, tuyere openings, as mentioned above, which 
support brick side-walls of the furnace, have proved successful 
for coal furnaces used for forging machine and drop-hammer 
heating, since they permit a great amount of work to be handled 
through their openings without wearing away as would a brick 
arch. Great care should be exercised properly to design them 
so that a minimum amount of the cold tuyere will be in contact 
with the interior of the furnace, and all interior portions possible 
should be covered by the bricks. However, a discussion of 
these points will hardly come in the flame-shield class, although 
they can be made to do a great deal toward relieving the excessive 
heat to be borne by the furnace worker. 

Flange Shields for Furnaces. — Such portable flame shields 
as the one illustrated in Fig. 96 may prove serviceable before 
furnaces required for plate work, where the doors are often only 
opened for a moment at a time. This shield can be placed far 
enough in front of the furnace, that it will be possible to work 
under it or around it, in removing bulky work from the furnace, 
and yet it will afford the furnace tender some relief from the 
excessive glare that will come out the wide-opened door. To 
have this shield of light weight so that it may be readily 
pushed aside when not wanted, the frame may be made up of 
pipe and fittings, and a piece of thin sheet steel fastened in the 
panel by rings about the frame. 

About the most disagreeable task in a heat-treating shop is 
the removal of the pots from the case-hardening furnaces; these 
must be handled at a bright red heat in order that their contents 
may be dumped into the quenching tank with a minimum- 
time contact with the air, and before they have cooled sufficiently 
to require reheating. Facing the heat before the large open 
doors of the majority of these furnaces, in a man-killing task 
even when the weather is moderately cool. The boxes soon 
become more or less distorted, and then even the best of lifting 
devices will not remove a hot pot without several minutes labor 
in front of the doors. 

In Fig. 97 is shown a method of arranging a shield on one 



198 THE WORKING OF STEEL 

type of charging and removing truck. This shield cannot 
afford more than a partial protection to the body of the furnace 
tender, because he must be able to see around it, and in some 
cases even push it partly through the door of the furnace, but 
even small as it is it may still afford some welcome protection. 
The great advantage in this case of having the shield on the 
truck instead of stationary in front of the furnace, is that it 
still affords protection as long as the hot pot is being handled 
through the shop on its way to the quenching tank. 

It might be interesting to many engaged in the heat-treating 
or case hardening of steel parts, to make a special note of the 
design of the truck that is illustrated in connection with the 
shield; the general form is shown although the actual details 
for the construction of such a truck are lacking; these being 
simple, may be readily worked out by anyone wishing to build 
one. This is considered to be one of the quickest and easiest 
operated devices for the removal of this class of work from the 
furnace. To be sure it may only be used where the floor of the 
furnace has been built level with the floor of the room, but many 
of the modern furnaces of this class are so designed. 

The pack-hardening pots are cast with legs, from two to three 
inches high, to permit the circulation of the hot gases, and so 
heat more quickly. Between these legs and under the body 
of the pot, the two forward prongs of the truck are pushed, 
tilting the outer handle to make these prongs as low as possible. 
The handle is then lowered and, as it has a good leverage, the pot 
is easily raised from the floor, and the truck and its load rolled 
out. 

Heating of Manganese Steel. — Another form of heat-treating 
furnace is that which is used for the heating of manganese and 
other alloy steels, which after having been brought to the proper 
heat are drawn from the furnace into an immediate quenching 
tank. With manganese steel in particular, the parts are so 
fragile and easily damaged while hot that it is frequent practice 
to have a sloping platform immediately in front of the furnace 
door down which the castings may slide into a tank below the 
floor level. Such a furnace with a quenching tank in front of 
its door is shown in Fig. 98. 

These tanks are covered with plates while charging the furnace, 
and the cold castings are placed in a moderately cool furnace 
Since some of these steels must not be charged into a furnace 
where the heat is extreme but should be brought up to their 



FURNACES 199 

final heat gradually, there is little discomfort during the charging 
process. When quenching, however, from a temperature of 
1,800° to 1,900°, it is extremely unpleasant in front of the doors. 
The swinging shield is here adapted to give protecton for this 
work. As will be noted it is hung a sufficient distance in front 
of the doors, that it may not interfere with the castings as they 
come from the furnace, and slide down into the tank. 

To facilitate the work, and avoid the necessity of working 
with the bars outside the edges of the shield, the slot-like hole 
is cut in the center of the shield, and through this the bars or 
rakes for dragging out the castings are easily inserted and 
manipulated. The advantage of such a swinging shield is that 
it may be readily moved from side to side, or forward and back 
as occasion requires. 

FURNACE DATA 

In order to give definite information concerning furnaces, 
fuels etc., the following data is quoted from a paper by Seth A 
Moulton and W. H. Lyman before the Steel Heat Treaters 
Society in September, 1920. 

This considers a factory producing 30,000 lb. of automobile 
gears per 24 hr. The transmission gears will be of high-carbon 
steel and the differential of low-carbon steel, carburized. The 
heat-treating equipment required is: 

1. Annealing furnaces 1,400 to 1,600°F. 

2. Carburizing furnaces 1,700 to 1,800°F. 

3. Hardening furnaces 1,450 to 1,550°F. 

4. Drawing furnaces 350 to 950°F. 

All of the forging blanks are annealed before machining, about 
three-quarters of the machined gears and parts are carburized, 
all the carburized gears are given a double treatment for core 
and case, all gears and parts are hardened and all parts are 
drawn. 

The possible sources of heat supply and their values are as 
follows : — 

1. Oil 140,000 B.t.u. per gallon 

2. Natural gas 1,100 B.t.u. per cubic foot 

3. City gas 650 B.t.u. per cubic foot 

4. Water gas 300 B.t.u. per cubic foot 

5. Producer gas 170 B.t.u. per cubic foot 

6. Coal 12,000 B.t.u. per pound 

7. Electric current 3,412 B.t.u. per kilowatt-hour 



200 



THE WORKING OF STEEL 



For the heat treatment specified only comparatively low 
temperatures are required. No difficulty will be experienced in 
attaining the desired maximum temperature of 1,800°F. with 
any of the heating medium above enumerated; but it should be 
noted that the producer gas with a B.t.u. content of 170 per cubic 
foot and the electric current would require specially designed fur- 
naces to obtain higher temperatures than 1800°F. 

Table 28. — Comparative Operating Costs 
Assuming 

Cost of oil- and gas-fired furnaces in- 
stalled as $100. 00 per square foot of hearth 

Cost of coal-fired furnace installed as . . 150 . 00 per square foot of hearth 
Cost of electric furnace 100 kw. capac- 
ity installed as 90 . 00 per kilowatt 

Cost of electric furnace 150 kw. capac- 
ity installed as 70 . 00 per kilowatt 

Output 3,000 lb. charge, 8 hr. heat carburizing, 2 hr. heating only. An- 
nual service 7,200 hr. Fixed charges including interest, depreciation, taxes, 
insurance and maintenance 15 per cent. Extra operating labor for coal- 
fired furnace 60 cts. per hour, one man four furnaces. 







Cost 


3F Various 


Types ot< 


Furnaces 










Class fuel 


Fuel per 
charge 


Unit fuel 
cost 


Installa- 
tion cost 


Effi- 
ciency, 
per 
cent 


Fixed 
charges 


Cost 

per 

charge 






1 


2 


3 


4 


5 


6 


7 




1 
2 
3 

4 
5 
6 

7 

1 
2 
3 
4 
5 
6 
7 


Oil 


52.0 gal. 

4.4 M 

8.3 M 

18.7 M 

37.3 M 

814.0 lb. 

500.0 kw-hr. 


$0.15 gat. 
0.50 M 
0.80 M 
0.40 
0.10 M 
6.00 ton 
0.015kw. 


$2,400.00 
2,400.00 
2,400.00 
2,400.00 
2,400.00 
3,600.00 
9,000.00 


12.6 
18.8 
17.0 
16.4 
14.5 
9.4 
53.0 


$.40 
0.40 
0.40 
0.40 
0.40 
0.60 
1.50 


$8.20 


.5 
°E 

u 
03 
O 


Natural gas. . . 

City gas 

Water gas 

Producer gas . . 

Coal 

Electricity 


2.60 
7.04 
7.88 
4.13 
3.98 
9.00 


CD 


Oil 

Natural gas. . . 

City gas 

Water gas 

Producer gas . . 
Coal 


30.8 gal. 
2.61 M 
4.9 M ' 
11.1 M 
22.1 M 
348.0 1b. 
329 . kw-hr. 


0.15 gal. 
0.50 M 
0.80 M 
0.40 M 
0.10 M 
6.00 ton 
0.015kw. 


2,400.00 
2,400.00 
2,400.00 
2,400.00 
2,400.00 
3,600.00 
10,500.00 


21.4 
32.0 
28.8 
27.6 
24.6 
22.0 
81.75 


0.10 
0.10 
0.10 
0.10 
0.10 
0.15 
0.44 


4.72 
1.40 
4.02 
4.54 
2.31 
1.38 




Electricity 


5.38 



This shows but two of the operations and for a single furnace. 
The total costs for all operations on the 30,000 lb. of gears per 
24 hr. is shown in Table 29. 



FURNACES 



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CHAPTER XII 
PYROMETRY AND PYROMETERS 

A knowledge of the fundamental principles of pyrometry, or 
the meausrement of temperatures, is quite necessary for one 
engaged in the heat treatment of steel. It is only by careful 
measurement and control of the heating of steel that the full 
benefit of a heat-treating operation is secured. 

Before the advent of the thermo-couple, methods of tempera- 
ture measurement were very crude. The blacksmith depended 
on his eyes to tell him when the proper temperature was reached, 
and of course the "color " appeared different on light or dark days. 
"Cherry" to one man was "orange" to another, and it was 
therefore almost impossible to formulate any treatment which 
could be applied by several men to secure the same results. 

One of the early methods of measuring temperatures was the 
"iron ball" method. In this method, an iron ball, to which a 
wire was attached, was placed in the furnace and when it had 
reached the temperature of the furnace, it was quickly removed 
by means of the wire, and suspended in a can containing a known 
quantity of water; the volume of water being such that the heat 
would not cause it to boil. The rise in temperature of the water 
was measured by a thermometer, and, knowing the heat capacity 
of the iron ball and that of the water, the temperature of the ball, 
and therefore the furnace, could be calculated. Usually a set 
of tables was prepared to simplify the calculations . The iron ball , 
however, scaled, and changed in weight with repeated use, making 
the determinations less and less accurate. A copper ball was 
often used to decrease this change, but even that was subject to 
error. This method is still sometimes used, but for really precise 
work, a platinum ball, which will not scale or change in weight, is 
necessary, and the cost of this ball, together with the slowness of 
the method, have rendered the practice obsolete except for armor 
plate as has been described. 

PYROMETERS 

Armor plate makers still use the copper ball or Siemens' 
water pyrometer because they can place a number of the balls or 

202 



PYROMETRY AND PYROMETERS 



203 



weights on the plate in locations where it is difficult to use other 
pyrometers. One of these pyrometers is shown in section in 
Fig. 99. 

Siemens' Water Pyrometer. — It consists of a cjdindrical copper 
vessel provided with a handle and containing a second smaller 
copper vessel with double walls. An air space a separates the 
two vessels, and a layer of felt the two walls of the inner one, in 
order to retard the exchange of temperature with the surround- 
ings. The capacity of the inner vessel is 
a little more than one pint. A mercury 
thermometer b is fixed close to the wall of 
the inner vessel, its lower part being pro- 
tected by a perforated brass tube, whilst 
the upper projects above the vessel and is 
divided as usual on the stem into degrees, 
Fahrenheit or Centigrade, as desired. At 
the side of the thermometer there is a 
small brass scale c, which slides up and 
down, and on which the high temperatures 
are marked in the same degrees as those in 
which the mercury thermometer is divided ; 
on a level with the zero division of the 
brass scale a small pointer is fixed, which 
traverses the scale of the thermometer. 

Short cylinders d, of either copper, iron 
or platinum, are supplied with the pyro- 
meter, which are so adjusted that their 
heat capacity at ordinary temperature is 
equal to one-fiftieth of that of the copper 
vessel filled with one pint of water. As, 
however, the specific heat of metals in- 
creases with the temperature, allowance 
is made on the brass sliding scales, which are divided according to 
the metal used for the pyrometer cylinder d. It will therefore be 
understood that a different sliding scaleis required for the particu- 
lar kind of metal of which a cylinder is composed. In order to 
obtain accurate measurements, each sliding scale must be used 
only in conjunction with its own thermometer, and in case the 
latter breaks a new scale must be made and graduated for the new 
thermometer. 

The water pyrometer is used as follows: 




Fig. 99. — Siemens' copper- 
ball pyrometer. 



204 THE WORKING OF STEEL 

Exactly one pint (0.568 liter) of clean water, perfectly distilled 
or rain water, is poured into the copper vessel, and the pyrometer 
is left for a few minutes to allow the thermometer to attain the 
temperature of the water. 

The brass scale c is then set with its pointer opposite the tem- 
perature of the water as shown by the thermometer. Meanwhile 
one of the metal cylinders has been exposed to the high tempera- 
ture which is to be measured, and after allowing sufficient time 
for it to acquire that temperature, it is rapidly removed and 
dropped into the pyrometer vessel without splashing any of the 
water out. 

The temperature of the water will rise until, after a little while, 
the mercury of the thermometer has become stationary. When 
this is observed the degrees of the thermometer are read off, as 
well as those on the brass scale c opposite the top of the mercury. 
The sum of these two values together gives the temperature of the 
flue, furnace or other heated space in which the metal cylinder had 
been placed. With cylinders of copper and iron, temperatures 
up to 1,800°F. (1000°C.) can be measured, but with platinum 
cylinders the limit is 2,700°F. (1,500°C). 

For ordinary furnace work either copper or wrought-iron 
cylinders may be used. Iron cylinders possess a higher melting- 
point and have less tendency to scale than those of copper, but 
the latter are much less affected by the corrosive action of the 
furnace gases; platinum is, of course, not subject to any of these 
disadvantages. 

The weight to which the different metal cylinders are adjusted 
is as follows: 

Copper 137.0 grams 

Wrought-iron 112.0 grams 

Platinum 402.6 grams 

In course of time the cylinders lose weight by scaling; but tables 
are provided giving multipliers for the diminished weights, by 
which the reading on the brass scale should be multiplied. 

THE THERMO-COUPLE 

With the application of the thermo-couple, the measurement of 
temperatures, between, say, 700 and 2,500°F., was made more 
simple and precise. The theory of the thermo-couple is simple; 
it is that if two bars, rods, or wires of different metals are joined 



PYROMETRY AND PYROMETERS 205 

together at their ends, when heated so that one junction is hotter 
than the other, an electromotive force is set up through the 
metals, which will increase with the increase of the difference of 
temperature between the two junctions. This electromotive 
force, or voltage, may be measured, and, from a chart previously 
prepared, the temperature determined. In most pyrometers, of 
course, the temperatures are inscribed directly on the voltmeter, 
but the fact remains that it is the voltage of a small electric 
current, and not heat, that is actually measured. 

There are two common types of thermo-couples, the first mak- 
ing use of common, inexpensive metals, such as iron wire and 
nichrome wire. This is the so-called "base metal" couple. The 
other is composed of expensive metals such as platinum wire, and 
a wire of an alloy of platinum with 10 per cent of rhodium or 
iridium. This is called the "rare metal" couple, and because its 
component metals are less affected by heat, it lasts longer, and 
varies less than the base metal couple. 

The cold junction of a thermo-couple may be connected by 
means of copper wires to the voltmeter, although in some installa- 
tions of base metal couples, the wires forming the couple are 
themselves extended to the voltmeter, making copper connections 
unnecessary. From the foregoing, it may be seen that accurately 
to measure the temperature of the hot end of a thermo-couple, 
we must know the temperature of the cold end, as it is the difference 
in the temperatures that determines the voltmeter readings. 
This is absolutely essential for precision, and its importance 
cannot be over-emphasized. 

When pyrometers are used in daily operation, they should be 
checked or calibrated two or three times a month, or even every 
week. Where there are many in use, it is good practice to have 
a master pyrometer of a rare metal couple, which is used only for 
checking up the others. The master pyrometer, after calibrating 
against the melting points of various substances, will have a 
calibration chart which should be used in the checking operation. 

It is customary now to send a rare metal couple to the Bureau 
of Standards at Washington, where it is very carefully calibrated 
for a nominal charge, and returned with the voltmeter readings of 
a series of temperatures covering practically the whole range of 
the couple. This couple is then used only for checking those in 
daily use. 

Pyrometer couples are more or less expensive, and should be 



206 THE WORKING OF STEEL 

cared for when in use. The wires of the couple should be insu- 
lated from each other by fireclay leads or tubes, and it is well to 
encase them in a fireclay, porcelain, or quartz tube to keep out 
the furnace gases, which in time destroy the hot junction. This 
tube of fireclay, or porcelain, etc., should be protected against 
breakage by an iron or nichrome tube, plugged or welded at the 
hot end. These simple precautions will prolong the life of a 
couple and maintain its precision longer. 

Sometimes erroneous temperatures are recorded because the 
"cold end" of the couple is too near the furnace and gets hot. 
This always causes a temperature reading lower than the actual, 
and should be guarded against. It is well to keep the cold end 
cool with water, a wet cloth, or by placing it where cool air will 
circulate around it. Best of all, is to have the cold junction in a 
box, together with a thermometer, so that its temperature may 
definitely be known. If this temperature should rise 20°F. on a 
hot day, a correction of 20°F. should be added to the pyrometer 
reading, and so on. In the most up-to-date installations, this 
cold junction compensation is taken care of automatically, a fact 
which indicates its importance. 

Optical pyrometers are often used where it is impracticable to 
use the thermo-couple, either because the temperature is so high 
that it would destroy the couple, or the heat to be measured is 
inaccessible to the couple of ordinary length. The temperatures 
of slag or metal in furnaces or running through tap-holes or 
troughs are often measured with optical pyrometers. 

In one type of optical pyrometer, the observer focuses it on the 
metal or slag and moves an adjustable dial or gage so as to get 
an exact comparison between the color of the heat measured with 
the color of a lamp or screen in the pyrometer itself. This, of 
course, requires practice, and judgment, and brings in the per- 
sonal equation. With care, however, very reliable temperature 
measurements may be made. The temperatures of rails, as they 
leave the finishing pass of a rolling mill, are measured in this way. 

Another type of optical pyrometer is focused on the body, the 
temperature of which is to be measured. The rays converge in 
the telescope on metal cells, heating them, and thereby generating 
a small electric current, the voltage of which is read on a cali- 
brated voltmeter similar to that used with the thermo-couple. 
The best precision is obtained when an optical pyrometer is used 
each time under similar conditions of light and the same observer. 



PYROMETRY AND PYROMETERS 207 

Where it is impracticable to use either thermo-couples or 
optical pyrometers. " sentinels" may be used. There are small 
cones or cylinders made of salts or other substances of known 
melting points and covering a wide range of temperatures. 

If six of these "sentinels," melting respectively at 1,300°, 
1,350°, 1,400°, 1,450°, 1,500°, and 1,550°F., were placed in a row 
in a furnace, together with a piece of steel to be treated, and the 
whole heated up uniformly, the sentinels would melt one by one 
and the observer, by watching them through an opening in the 
furnace, could tell when his furnace is at say 1,500° or between 
1,500° and 1,550°, and regulate the heat accordingly. 

A very accurate type of pyrometer, but one not so commonly 
used as those previously described, is the resistance pyrometer. 
In this type, the temperature is determined by measuring the 
resistance to an electric current of a wire which is at the heat to 
be measured. This wire is usually of platinum, wound around a 
quartz tube, the whole being placed in the furnace. When the 
wire is at the temperature of the furnace, it is connected by wires 
with a Wheatstone Bridge, a delicate device for measuring 
electrical resistance, and an electric current is passed through the 
wire. This current is balanced by switching in resistances in the 
Wheatstone Bridge, until a delicate electrical device shows that 
no current is flowing. The resistance of the platinum wire at the 
heat to be measured is thus determined on the '' Bridge," and the 
temperature read off on a calibration chart, which shows the 
resistance at various temperatures. 

These are the common methods used to-day for measuring tem- 
peratures, but whatever method is used, the observer should bear 
in mind that the greatest precision is obtained, and hence the 
highest efficiency, by keeping the apparatus in good working 
order, making sure that conditions are the same each time, and 
calibrating or checking against a standard at regular intervals. 

THE PYROMETER AND ITS USE 

In the heat treatment of steel, it has become absolutely neces- 
sary that a measuring instrument be used which will give the 
operator an exact reading of heat in furnace. There are a number 
of instruments and devices manufactured for this purpose but any 
instrument that will not give a direct reading without any guess 
work should have no place in the heat-treating department. 

A pyrometer installation is very simple and any of the leading 



208 THE WORKING OF STEEL 

makers will furnish diagrams for the correct wiring and give 
detailed information as to the proper care of, and how best to use 
their particular instrument. There are certain general principles, 
however, that must be observed by the operator and it cannot be 
too strongly impressed upon them that the human factor involved 
is always the deciding factor in the heat treatment of steel. 

A pyrometer is merely an aid in the performance of doing good 
work, and when carefully observed will help in giving a uniformity 
of product and act as a check on careless operators. The oper- 
ator must bear in mind that although the reading on the pyro- 
meter scale gives the direct heat of furnace where pyrometer-rod 
or "py-rod" is inserted, it will not give the temperature of the 
work in furnace, unless by predetermined tests, the heat for 
penetrating a certain bulk of material has been decided on, and 
the time necessary for such penetration is known. 

Each quality of steel, made up of separate analyses, needs a 
certain heat to determine its critical point, and the elements of 
which the steel is composed carries a certain time limit which is 
necessary for the thorough solution of such elements in and above 
the critical point of temperature. When all these factors are 
known, and standards set, a pyrometer and clock, with an oper- 
ator willing to work to orders given, no trouble will arise in the 
proper heat treatment of steel. 

Experience has taught us that the time factor is of greater 
importance than the exact reading of temperature, as fortunately 
the limits between the critical range, i.e., the decalescent vs. 
recalescent point has a wide variation, but the time limit for the 
soaking or solution point of the elements is practically a constant 
factor, therefore, a clock is as necessary to the proper pyrometer 
equipment as the pyrometer itself. 

For the purpose of general work where a wide range of steels 
or a variable treatment is called for, it becomes necessary to 
have the pyrometer calibrated constantly, and when no master 
instrument is kept for this purpose the following method can be 
used to give the desired results : 

CALIBRATION OF PYROMETER WITH COMMON SALT 

An easy and convenient method for standardization and one 
which does not necessitate the use of an expensive laboratory 
equipment is that based upon determining the melting point of 
common table salt (sodium chloride). While theoretically salt 



PYROMETRY AND PYROMETERS 209 

that is chemically pure should be used (and this is neither expen- 
sive nor difficult to procure), commerical accuracy may be ob- 
tained by using common table salt such as is sold by every grocer. 
The salt is melted in a clean crucible of fireclay, iron or nickel, 
either in a furnace or over a forge-fire, and then further heated 
until a temperature of about 1,600 to 1,650°F. is attained. It is 
essential that this crucible be clean because a slight admixture of 
a foreign substance might noticeably change the melting point. 

The thermo-couple to be calibrated is then removed from its 
protecting tube and its hot end is immersed in the salt bath. 
When this end has reached the temperature of the bath, the 
crucible is removed from the source of heat and allowed to cool, 
and cooling readings are then taken every 10 sec. on the milli- 
voltmeter or pyrometer. A curve is then plotted by using time 
and temperature as coordinates, and the temperature of the 
freezing point of salt, as indicated by this particular thermo- 
couple, is noted, i.e., at the point where the temperature of the 
bath remains temporarily constant while the salt is freezing. 
The length of time during which the temperature is stationary 
depends on the size of the bath and the rate of cooling, and is not 
a factor in the calibration. The melting point of salt is 1,472°F., 
and the needed correction for the instrument under observation 
can be readily applied. 

It should not be understood from the above, however, that the 
salt-bath calibration cannot be made without plotting a curve; in 
actual practice at least a hundred tests are made without plotting 
any curve to one in which it is done. The observer, if awake, 
may reasonably be expected to have sufficient appreciation of the 
lapse of time definitely to observe the temperature at which the 
falling pointer of the instrument halts. The gradual dropping of 
the pointer before freezing, unless there is a large mass of salt, 
takes place rapidly enough for one to be sure that the temperature 
is constantly falling, and the long period of rest during freezing 
is quite definite. The procedure of detecting the solidification 
point of the salt by the hesitation of the pointer without plotting 
any curve is suggested because of its simplicity. 

Complete Calibration of Pyrometers. — For the complete cali- 
bration of a thermo-couple of unknown electromotive force, 
the new couple may be checked against a standard instrument, 
placing the two bare couples side by side in a suitable tube and 
taking frequent readings over the range of temperatures desired. 

14 



210 



THE WORKING OF STEEL 



If only one instrument, such as a millivoltmeter, is available, 
and there is no standard couple at hand, the new couple may be 
calibrated over a wide range of temperatures by the use of the 
following standards : 

Water, boiling point 212°F. 

Tin, under charcoal, freezing point 450°F. 

Lead, under charcoal, freezing point 621°F. 

Zinc, under charcoal, freezing point 786°F. 

Sulphur, boiling point 832°F. 

Aluminum, under charcoal, freezing point. . . . 1,216°F. 

Sodium chloride (salt), freezing point. 1,474°F. 

Potassium sulphate, freezing point 1,958°F. 

A good practice is to make one pyrometer a standard; calibrate 
it frequently by the melting-point-of-salt method, and each morn- 
ing check up every pyrometer in the works with the standard, 
making the necessary corrections to be used for the day's work. 
By pursuing this course systematically, the improved quality 
of the product will much more than compensate for the extra 
work. 

The purity of the salt affects its freezing or melting point. 
Different authorities give temperatures varying by 50°. It is 
suggested that a sufficient quantity for an extended period of 
salt be secured. Test the melting point with a pyrometer of 
known accuracy. Knowing this temperature it will be easy to 
calibrate other pyrometers. The salt should be kept free from 
dirt and other additional impurities. 

Placing of Pyrometers. — When installing pyrometer, care 
should be taken that it is not placed within direct heat of furnace 
or furnaces, as this would have the effect of not giving a true 
reading. When calibrating such an instrument, the potential 
drop in voltage must be figured, and such drop must be added to 
heat wanted. 

When having multiple connections, in other words, when a 
number of furnaces are connected up in series, and multiple 
switch is used for control, it becomes apparent that, for uni- 
formity of product from each furnace, the furnaces furthest away 
from the reading instrument must have potential drop figured out 
correctly. 

This calibration can be done by connecting the master instru- 
ment with each furnace separately, and watch reading given on 
pyrometer connected with multiple switch. In this connection, 



PYROMETRY AND PYROMETERS 211 

be sure that cold junction point has been tested, and is in perfect 
working condition. 

Py-rods should be tested very often, and it is important that 
no foreign substance is allowed to freeze in the tube, so that 
enclosed point becomes a part of a solid mass with outside pro- 
tecting tube. Wires over the furnaces must be carefully in- 
spected from time to time, as no true reading can be had on 
instrument, if insulation is burned off. 

Where standard calibrating instrument is used, the dry battery 
in connection with them should be tested before using, so as to 
be sure that both amperes and voltage is correct. 

THE LEEDS AND NORTHRUP POTENTIOMETER SYSTEM 

The potentiometer pyrometer system is both flexible and sub- 
stantial in that it is not affected by the jar and vibration of the fac- 
tory or the forge shop. Large or small couples, long or short 
leads can be used without adjustment. The recording instru- 
ment may be placed where it is most convenient, without regard 
to the distance from the furnace. 

Its Fundamental Principle. — The potentiometer is the elec- 
trical equivalent of the chemical balance, or balance arm scales. 
Measurements are made with balance scales by varying known 
weights until they equal the unknown weight. When the two 
are equal the scales stand at zero that, is, in the position which 
they occupy when there is no weight on either pan; the scales 
are then said to be balanced. Measurements are made with 
the potentiometer by varying a known electromotive force until 
it equals the unknown; when the two are equal the index of the 
potentiometer, the galvanometer needle, stands motionless as it 
is alternately connected and disconnected. The variable known 
weights are units separate from the scales, but the potentiometer 
provides its own variable known electromotive force. 

The potentiometer provides, first, a means of securing a known 
variable electromotive force and, second, suitable electrical con- 
nections for bringing that electromotive force to a point where it 
may be balanced against the unknown electromotive force of the 
couple. The two are connected with opposite polarity, or so 
that the two e.m.f.s oppose one another. So long as one is 
stronger than the other a current will flow through the couple; 
when the two are equal no current will flow. 

Figure 100 shows the wiring of the potentiometer in its simplest 



212 



THE WORKING OF STEEL 



form. The thermo-couple is at H, with its polarity as shown by 
the symbols + and — . It is connected with the main circuit of 
the potentiometer at the fixed point D and the point G. 

A current from the dry cell Ba is constantly flowing through 
the main, or so-called potentiometer circuit, ABCDGEF. The 
section DGE of this circuit is a slide wire, uniform in resistance 




Fig. 100. — Simple potentiometer. 

throughout its length. The scale is fixed on this slide wire. The 
current from the cell Ba as it flows through DGE, undergoes a fall 
in potential, setting up a difference in voltage, that is, an elec- 
tromotive force, between D and E. There will also be electro- 
motive force between D and all other points on the slide wire. 




Fig. 101. — Standard cell potentiometer. 

The polarity of this is in opposition to the polarity of the thermo- 
couple which connects into the potentiometer at D and at G. 
By moving G along the slide wire a point is found where the 
voltage between D and G in the slide wire is just equal to the 
voltage between D and G generated by the thermo-couple. A gal- 
vanometer in the thermo-couple circuit indicates when the 



PYROMETRY AND PYROMETERS 



213 



balance point is reached, since at this point the galvanometer 
needle will stand motionless when its circuit is opened and closed. 

The voltage in the slide wire will vary with the current flowing 
through it from the cell Ba and a means of standardizing this is 
provided. SC, Fig. 101, is a cadmium cell whose voltage is con- 
stant. It is connected at two points C and D to the potentiometer 
circuit whenever the potentiometer current is to be standardized. 
At this time the galvanometer is thrown in series with SC. The 
variable rheostat R is then adjusted until the current flowing is 
such that as it flows through the standard resistance CD, the fall 
in potential between C and D is just equal to the voltage of the 
standard cell SC. At this time the galvanometer will indicate 
a balance in the same way as when it was used with a thermo- 
couple. By this operation the current in the slide wire DGE has 
been standardized. 

Development of the Wiring Scheme of the Cold-end Compen- 
sator. — The net voltage generated by a thermo-couple depends 




Fig. 102. — Hand adjusted cold-end compensator. 



upon the temperature of the hot end and the temperature of the 
cold end. Therefore, any method adopted for reading tempera- 
ture by means of thermo-couples must in some way provide a 
means of correcting for the temperature of the cold end. The 
potentiometer may have either of two very simple devices 
for this purpose. In one form the operator is required to set a 
small index to a point on a scale corresponding to the known cold 
junction temperature. In the other form an even more simple 
automatic compensator is employed. The principle of each is 
described in the succeeding paragraphs, in which the assumption 
is made that the reader already understands the potentiometer 
principle as described above. 



214 



THE WORKING OF STEEL 



As previously explained the voltage of the thermo-couple is 
measured by balancing it against the voltage drop DG in the 
potentiometer. 

As shown in Fig. 101, the magnitude of the balancing voltage 
is controlled by the position of G. Make D movable as shown in 
Fig. 102 and the magnitude of the voltage DG may be varied 
either from the point D or the point G. This gives a means of 
compensating for cold end changes by setting the slider D. As 
the cold end temperature rises the net voltage generated by the 
couple decreases, assuming the hot end temperature to be con- 
stant. To balance this decreased voltage the slider D is moved 
along its scale to a new point nearer G. In other words, the 
slider D is moved along its scale until it corresponds to the known 
temperature of the cold end and then the potentiometer is bal- 




Fig. 103.— Another type of compensator. 



anced by moving the slider G. The readings of G will then be 
direct 

The same results will be obtained if a slide wire upon which D 
bears is in parallel with the slide wire of G, as shown in Fig. 103. 

Automatic Compensator. — It should be noted that the effect 
of moving the contact D, Fig. 103, is to vary the ratio of the 
resistances on the two sides of the point D in the secondary slide 
wire. In the recording pyrometers, an automatic compensator 
is employed. This automatic compensator varies the ratio on 
the two sides of the point D in the following manner : 

The point D, Fig. 104, is mechanically fixed; on one side of D 
is the constant resistance coil M, on the other the nickel coil N. 
N is placed at or near the cold end of the thermo-couple (or 
couples). Nickel has a high temperature coefficient and the 
electrical proportions of M and N are such that the resistance 



PYROMETRY AND PYROMETERS 



215 



change of N, as it varies with the temperature of the cold end, has 
the same effect upon the balancing voltage between D and G 
that the movement of the point D, Fig. 104, has in the hand- 
operated compensator. 

Instruments embodying these principles are shown in Figs. 
105 to 107. The captions making their uses clear. 




Fig. 104. — Automatic cold-end compensator. 

PLACING THE THERMO-COUPLES 

The following illustrations from the Taylor Instrument 
Company show different applications of the thermo-couples to 




Fig. 105. — Potentiometer ready for use. 

furnaces of various kinds. Figure 108 shows an oil-fired furnace 
with a simple vertical installation. Figure 109 shows a method 



216 



THE WORKING OF STEEL 



of imbedding the thermo-couple in the floor of a furnace so as to 
require no space in the heating chamber. 

Two methods of applying a pyrometer to a gas furnace are 
shown in Fig. 110. The vertical method is to be preferred in 




Fig. 106. — Eight-point recording pyrometer — Carpenter Steel Co. 



most cases. Figure 111 shows how to connect four furnaces to 
one pyrometer and recording equipment. Figure 112 is a simple 
application to a lead or babbit tank. 

The instrument is light and portable, and can be sighted as 



PYROMETRY AND PYROMETERS 



217 




Fig. 107. — Multiple-point thermocouple recorder — Bethlehem Steel Co. 




SIDE ELEVATION-(SECTIONAL) 



FRONT ELEVATION 



Fig. 108. — Tycos pyrometer in oil-fired furnace. 



218 



THE WORKING OF STEEL 



easily as an opera glass. The telescope, which is held in the 
hand, weighs on 25 oz.; and the case containing the battery, 




**PROVEP_ BY- 



Fig. 109. — Thermocouple in floor of furnace. 




Fig. 110. — Pyrometer in gas furnace. 

rheostat and milliammeter, which is slung from the shoulder, 
only 10 lb. 

A large surface to sight at is not required. So long as the 
image formed by the objective is broader than the lamp fila- 
ment, the temperature can be measured accurately. 



PYROMETRY AND PYROMETERS 



219 




Fig. 111. — Tycos multiple indicating pyrometer and recorder. 



INDICATOR 




METAL BATH- 



TO INDICATOR' 









Fig. 112. — Pyrometer in galvanizing tank. 



220 



THE WORKING OF STEEL 



Distance does not matter, as the brightness of the image 
formed by the lens is practically constant, regardless of the 
distance of the instrument from the hot object. 

The manipulation is simple and rapid, consisting merely in 
the turning of a knurled knob. The setting is made with great 
precision, due to the rapid change in light intensity with change 

LAMP 



oajecrwa 




w\Aaaa 



Fig. 113. — Leeds & Northrup optical pyrometer. 

in temperature and to the sensitiveness of the eye to differ- 
ences of light intensity. In the region of temperatures used 
for hardening steel, for example, different observers using the 
instrument will agree within 3°C. 

Only brightness, not color, of light is matched, as light of 
only one color reaches the eye. Color blindness, therefore, is 






Fig. 114.— Too low. Fig. 115. — Too high. Fig. 116.— Correct. 

no hindrance to the use of this method. The use of the instru- 
ment is shown in Fig. 117. 

Optical System and Electrical Circuit of the Leeds & Northrup 
Optical Pyrometer. — For extremely high temperature, the optical 
pyrometer is largely used. This is a comparative method. By 
means of the rheostat the current through the lamp is adjusted 



PYROMETRY AXD PYROMETERS 



221 



until the brightness of the filament is just equal to the brightness 
of the image produced by the lens L, Fig. 113, whereupon the 
filament blends with or becomes indistinguishable in the back- 
ground formed by the image of the hot object. This adjustment 
can be made with great accuracy and certainty, as the effect of 
radiation upon the eye varies some twenty times faster than does 
the temperature at 1,600°F., and some fourteen times faster at 
3,400°F. When a balance has been obtained, the observer notes 
the reading of the milliammeter. The temperature correspond- 
ing to the current is then read from a calibration curve supplied 
with the instrument. 




Fig. 117. — Using the optical pyrometer. 



As the intensity of the light emitted at the higher temperatures 
becomes dazzling, it is found desirable to introduce a piece of red 
glass in the eye piece at R. This also eliminates any question of 
matching colors, or of the observer's ability to distinguish colors. 
It is further of value in dealing with bodies which do not radiate 
light of the same composition as that emitted by a black body, 
since nevertheless the intensity of radiation of any one color from 



222 . THE WORKING OF STEEL 

such bodies increases progressively in a definite manner as the 
temperature rises. The intensity of this one color can therefore 
be used as a measure of temperature for the body in question. 
Figures 114 to 116 show the way it is read. 

CORRECTION FOR COLD-JUNCTION ERRORS 

The voltage generated by a thermo-couple of an electric 
pyrometer is dependent on the difference in temperature be- 
tween its hot junction, inside the furnace, and the cold junc- 
tion, or opposite end of the thermo-couple to which the copper 
wires are connected. If the temperature of this cold junction 
rises and falls, the indications of the instrument will vary, 
although the hot junction in the furnace may be at a constant 
temperature. 

A cold-junction temperature of 75°F., or 25°C, is usually 
adopted in commercial pyrometers, and the pointer on the 
pyrometer should stand at this point on the scale when the 
hot junction is not heated. If the cold-junction temperature 
rises about 75°F., where base metal thermo-couples are used, 
the pyrometer will read approximately 1° low for every 1° rise 
in temperature above 75°F. For example, if the instrument is 
adjusted for a cold-junction temperature of 75°, and the actual 
cold-junction temperature is 90°F., the pyrometer will read 
15° low. If, however, the cold-junction temperature falls 
below 75°F., the pyrometer will read high instead of low, 
approximately 1° for every 1° drop in temperature below 75°F. 

With platinum thermo-couples, the error is approximately 
]>4° for 1° change in temperature. 

Correction by Zero Adjustment. — Many pyrometers are 
supplied with a zero adjuster, by means of which the pointer 
can be set to any actual cold-junction temperature. If the 
cold junction of the thermo-couple is in a temperature of 100°F., 
the pointer can be set to this point on the scale, and the readings 
of the instrument will be correct. 

Compensating Leads. — By the use of compensating leads, 
formed of the same material as the thermo-couple, the cold 
junction can be removed from the head of the thermo-couple 
to a point 10, 20 or 50 ft. distant from the furnace, where the 
temperature is reasonably constant. Where greater accuracy 
is desired, a common method is to drive a 2-in. pipe, with a 
pointed closed end, some 10 to 20 ft. into the ground, as shown 



PYROMETRY AND PYROMETERS 



223 



in Fig. 118. The compensating leads are joined to the copper 
leads, and the junction forced down to the bottom of the pipe. 
The cold junction is now in the ground, beneath the building, 
at a depth at which the temperature is very constant, about 
70°F., throughout the year. This method will usually control 
the cold-junction temperature within 5°F. 

Where the greatest accuracy is desired a compensating box 
will overcome cold-junction errors entirely. It consists of a 
case enclosing a lamp and thermostat, which can be adjusted 




Fig. 118. — Correcting cold-junction error. 

to maintain any desired temperature, from 50 to 150°F. The 
compensating leads enter the box and copper leads run from 
the compensating box to the instrument, so that the cold junction 
is within the box. Figure 119 shows a Brown compensating 
box. 

If it is desired to maintain the cold junction at 100°: the 
thermostat is set at this point, and the lamp, being wired to the 
110- or 220-volt lighting circuit, will light and heat the box until 
100° is reached, when the thermostat will open the circuit and 



224 



THE WORKING OF STEEL 



the light is extinguished. The box will now cool down to 98°, 
when the circuit is again closed, the lamp lights, the box heats 
up, and the operation is repeated. These will compensate for 
a number of thermo-couples. 




Fig. 119. — Compensating box. 

BROWN AUTOMATIC SIGNALING PYROMETER 

In large heat-treating plants it has been customary to maintain 
an operator at a central pyrometer, and by colored electric 




Fig. 120. — Brown automatic signaling pyrometer. 

lights at the furnaces, signal whether the temperatures are 
correct or not. It is common practice to locate three lights 
above each furnace — red, white and green. The red light 
burns when the temperature is too low, the white light when the 
temperature is within certain limits — for example, 20°F. of the 
correct temperature — and the green light when the temperature 
is too high. 

Instruments to operate the lights automatically have been 



PYROMETRY AND PYROMETERS 



225 



devised and one made by Brown is shown in Fig. 120. The 
same form of instrument is used for this purpose to auto- 
matically control furnace temperatures, and the pointer is 
depressed at intervals of every 10 sec. on contacts corresponding 
to the red, white and green lights. 




Fig. 121.— Automatic temperature control. 
AN AUTOMATIC TEMPERATURE CONTROL PYROMETER 

Automatic temperature control instruments are similar to 
the Brown indicating high resistance pyrometer with the excep- 
tion that the pointer is depressed at intervals of every 10 sec. 
upon contact-making devices. No current passes through the 
pointer which simply depresses the upper contact device tipped 
with platinum, which in turn comes in contact with the lower 
contact device, platinum-tipped, and the circuit is completed 
through these two contacts. The current is very small, about 

15 



226 



THE WORKING OF STEEL 



}?{o amp., as it is only necessary to operate the relay which in 
turn operates the switch or valve. A small motor is used to 
depress the pointer at regular intervals. The contact-making 
device is adjustable throughout the scale range of the instru- 
ment, and an index pointer indicates the point on the in- 
strument at which the temperature is being controlled. The 
space between the two contacts on the high and low side, 





Fig. 122. — Portable thermocouple testing molten brass. 

separated by insulating material, is equivalent to 1 per cent 
of the scale range. A control of temperature is therefore pos- 
sible within 1 per cent of the total scale range. Figure 121 
shows this attached to a small furnace. 



PYROMETERS FOR MOLTEN METAL 

Pyrometers for molten metal are connected to portable 
thermo-couples as in Fig. 122. Usually the pyrometer is port- 
able, as shown in this case which is a Brown. Other methods 
of mounting for this kind of work are shown in Figs. 123 to 124. 
The bent mountings designed for molten metal, such as brass 
or copper and is supplied with either clay, graphite or carborun- 
dum tubes. Fifteen feet of connecting wire is usually supplied. 

The angle mountings, Fig. 124, are recommended for baths 
such as lead or cyanide. The horizontal arm is usually about 
14 in. long, and the whole mounting is easily taken apart making 



PYROMETRY AND PYROMETERS 227 

replacements very easy. Details of the thermo-couple shown 
in Fig. 122 are given in Fig. 125. This is a straight rod with a 
protector for the hand of the operator. The lag in such couples 
is less than one minute. These are Englehard mountings. 

PROTECTORS FOR THERMO-COUPLES 

Thermo-couples must be protected from the danger of mechan- 
ical injury. For this purpose tubes of various refractory 
materials are made to act as protectors. These in turn are 
usually protected by outside metal tubes. Pure wrought iron 
is largely used for this purpose as it scales and oxidizes very 




Fig. 123. — Bent handle thermocouple with protector. 

slowly. These tubes are usually made from 2 to 4 in. shorter 
than the inner tubes. In lead baths the iron tubes often have 
one end welded closed and are used in connection with an angle 
form of mounting. 

Where it is necessary for protecting tubes to project a con- 
siderable distance into the furnace or tube made of nichrome 
is frequently used. This is a comparatively new alloy which 
stands high temperatures without bending. It is more costly 
than iron but also much more durable. 

When used in portable work and for high temperatures, 
pure nickel tubes are sometimes used. There is also a special 
metal tube made for use in cyanide. This metal withstands 
the intense penetrating characteristics of cyanide. It lasts from 
six to ten months as against a few days for the iron tube. 



228 



THE WORKING OF STEEL 



The inner tubes of refractory materials, also vary according 
to the purposes for which they are to be used. They are as 
follows : 

Marquardt mass tubes for temperatures up to 3,000°F., but 
they will not stand sudden changes in temperature, such as in 
contact with intermittent flames, without an extra outer covering 
of chamotte, fireclay or carborundum. 




Fig. 124. — Other styles of bent mounting. 



Fused silica tubes for continuous temperatures up to 1,800°F. 
and intermittently up to 2,400°F. The expansion at various 
temperatures is very small, which makes them of value for 
portable work. They also resist most acids. 

Chamotte tubes are useful up to 2,800°F. and are mechanically 
strong. They have a small expansion and resist temperature 



PYROMETRY AND PYROMETERS 229 

changes well, which makes them good as outside protectors for 
more fragile tubes. They cannot be used in molten metals, or 
baths of any kind nor in gases of an alkaline nature. They are 
used mainly to protect a Marquardt mass or silica tube. 

Carborundum tubes are also used as outside protection to 
other tubes. They stand sudden changes of temperature well 
and resist all gases except chlorine, above 1,750°F. Especially 
useful in protecting other tubes against molten aluminum, 
brass, copper and similar metals. 

Clay tubes are sometimes used in large annealing furnaces 
where they are cemented into place, forming a sort of well for 
the insertion of the thermo-couple. They are also used with 
portable thermo-couples for obtaining the temperatures of 
molten iron and steel in ladles. Used in this way they are 
naturally short-lived, but seem the best for this purpose. 




Fig. 125. — Straight thermocouple and guard. 

Corundite tubes are used as an outer protection for both the 
Marquardt mass and the silica tubes for kilns and for glass fur- 
naces. Graphite tubes are also used in some cases for outer 
protections. 

Calorized tubes are wrought iron pipe treated with no alumi- 
num oxide which often doubles or even triples the life of the tube 
at high temperature. 

These tubes come in different sizes and lengths depending on 
the uses for which they are intended. Heavy protecting outer 
tubes may be only 1 in. in inside diameter and as much as 3 in. 
outside diameter, while the inner tubes, such as the Marquardt 
mass and silica tubes are usually about % in. outside and % in. 
inside diameter. The length varies from 12 to 48 in. in most 
cases. 

Special terminal heads are provided, with brass binding posts 
for electrical connections, and with provisions for water cooling 
when necessary. 



APPENDIX 

Table 32. —Temperature Conversion Tables. 

Table 33.— Comparison Between Degrees Centigrade and Degrees 
Fahrenheit. 

Table 34. — Weight of Round, Octagon and Square Carbon Tool Steel 
per Foot. 

Table 35. — Weight of Round Carbon Tool Steel 12 In. in Diameter and 
Larger, per Foot. 

Table 36. — Decimal Equivalents of a foot. 

AUTHORITIES QUOTED 



231 



232 



THE WORKING OF STEEL 



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PY ROME TRY AND PYROMETERS 



233 



«0>(inOI)50TjNOC()0'tlMOCOOi'NOI»10fn 
HCOlONOlONinOOOOHniONOO "" 
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cocococococococo 



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234 



THE WORKING OF STEEL 



Those using pyrometers will find this and the preceding 
conversion table of great convenience: 



Table 33. — Comparison Between Degrees Centigrade and 
Degrees Fahrenheit 



Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


-40 


-40.0 


3 


-16.1 


40 


7.7 


89 


31.6 


132 


55.5 


175 


79.4 


275 


135.0 


-39 


-39.4 


4 


-15.5 


47 


8.3 


90 


32.2 


133 


56.1 


176 


80.0 


300 


148.8 


-38 


-38.8 


5 


-15.0 


48 


8.8 


91 


32.7 


134 


56.6 


177 


80.5 


325 


162.7 


-37 


-38.3 


6 


-14.4 


4!) 


9.3 


92 


33.3 


135 


57.2 


178 


81.1 


350 


176.6 


-36 


-37.7 


7 


-13.8 


50 


10.0 


93 


33.9 


136 


57.7 


179 


81.6 


375 


190.5 


-35 


-37.2 


8 


-13.3 


51 


10.5 


94 


34.4 


137 


58.3 


180 


82.2 


400 


204.4 


-34 


-36.6 


9 


-12.7 


52 


11.1 


95 


35.0 


138 


58.8 


181 


82.7 


425 


218.3 


-33 


-36.1 


10 


-12.2 


53 


11.6 


96 


35.5 


139 


59.4 


182 


83.3 


450 


232.2 


-32 


-35.5 


1J 


-11.6 


54 


12.2 


97 


36.1 


140 


60.0 


183 


83.8 


475 


246.1 


-31 


-35.0 


12 


-11.1 


55 


12.7 


98 


36.6 


141 


60.5 


184 


84.4 


500 


260.0 


-30 


-34.4 


18 


-10.5 


56 


13.3 


99 


37.2 


142 


61.1 


185* 


85.0 


525 


273.8 


-29 


-33.9 


14 


-10,0 


57 


13.8 


100 


37.7 


143 


61.6 


186 


85.5 


550 


287.7 


-28 


-33.3 


15 


- 9.3 


58 


14.4 


101 


38.3 


144 


62.2 


187 


86.1 


575 


301.6 


-27 


-32.7 


10 


- 8.8 


59 


15.0 


102 


38.8 


145 


62.7 


188 


86.6 


600 


315.5 


-26 


-32.2 


17 


- 8.3 


GO 


15.5 


103 


39.4 


146 


63.3 


189 


87.2 


625 


329.4 


-25 


-31.6 


IS 


- 7.7 


01 


16.1 


104 


40.0 


147 


63.8 


190 


87.7 


650 


343.3 


-24 


-31.1 


19 


- 7.2 


02 


16.6 


105 


40.5 


148 


64.4 


191 


88.3 


675 


357.2 


-23 


-30.5 


20 


- 6.6 


63 


17.2 


106 


41.1 


149 


65.0 


192 


88.8 


700 


371.1 


-22 


-30.0 


21 


- 6.1 


64 


17.7 


107 


41.6 


150 


65.5 


193 


89.4 


725 


385.0 


-21 


-29.4 


22 


- 5.5 


65 


18.3 


108 


42.2 


151 


66.1 


194 


90.0 


750 


398.8 


-20 


-28.8 


23 


- 5.0 


66 


18.8 


109 


42.7 


152 


66.6 


195 


90.5 


775 


412.7 


-19 


-28.3 


24 


- 4.4 


67 


19.4 


110 


43.3 


153 


67.2 


196 


91.1 


800 


426.6 


-18 


-27.7 


25 


- 3.8 


68 


20.0 


111 


43.8 


154 


67.7 


197 


91.6 


825 


440.5 


-17 


-27.2 


20 


- 3.3 


69 


20.5 


112 


44.4 


155 


68.3 


198 


92.2 


850 


454.4 


-16 


-26.6 


27 


- 2.7 


70 


21.1 


113 


45.0 


156 


68.8 


199 


92.7 


875 


468.3 


-15 


-26.1 


28 


- 2.2 


71 


21.6 


114 


45.5 


157 


69.4 


200 


93.3 


900 


482.2 


-14 


-25.5 


29 


- 1.6 


72 


22.2 


115 


46.1 


158 


70.0 


201 


93.8 


925 


496.1 


-13 


-25.0 


30 


- 1.1 


73 


22.7 


116 


46.6 


159 


70". 5 


202 


94.4 


950 


510.0 


-12 


-24.4 


31 


- 0.5 


74 


23.3 


117 


47.2 


160 


71.1 


203 


95.0 


975 


523.8 


-11 


-23.8 


32 


- 0.0 


75 


23.8 


118 


47.7 


161 


71.6 


204 


95.5 


1,000 


537.7 


-10 


-23.3 


33 


+ 0.5 


70 


24.4 


119 


48.3 


162 


72.2 


205 


96.1 


1,100 


593.3 


- 9 


-22.7 


34 


1.1 


77 


25.0 


120 


48.8 


163 


72.7 


206 


96.6 


1,200 


648.8 


- 8 


-22.2 


35 


1.6 


78 


25.5 


121 


49.4 


164 


73.3 


207 


97.2 


1,300 


704.4 


- 7 


-21.6 


36 


2.2 


79 


26.1 


122 


50.0 


165 


73.8 


208 


97.7 


1,400 


760.0 


- 6 


-21.1 


37 


2.7 


80 


26.6 


123 


50.5 


166 


74.4 


209 


98.3 


1,500 


815.5 


- 5 


-20.5 


38 


3.3 


81 


27.2 


124 


51.1 


167 


75.0 


210 


98.8 


1,600 


871.1 


- 4 


-20.0 


39 


3.8 


82 


27.7 


125 


51.6 


168 


75.5 


211 


99.4 


1,700 


926.6 


- 3 


-19.4 


40 


4.4 


83 


28.3 


126 


52.2 


169 


76.1 


212 


100.0 


1,800 


982.2 


- 2 


-18.8 


41 


5.0 


84 


28.8 


127 


52.7 


170 


76.6 


213 


100.5 


1,900 


1,037.7 


- 1 


-18.3 


42 


5.5 


85 


29.4 


128 


53.3 


171 


77.2 


214 


101.1 


2,000 


1,093.3 





-17.7 


43 


6.1 


80 


30.0 


129 


53.8 


172 


77.7 


215 


101.6 


2,100 


1,148.8 


+ 1 


-17.2 


44 


6.6 


87 


30.5 


130 


54.4 


173 


78.3 


225 


107.2 


2,200 


1,204.4 


2 


-16.6 


45 


7.2 


88 


31.1 


131 


55.0 


174 


78.8 


250 


121.1 


2,300 


1,260.0 



9 x degrees C. 
Degrees Fahrenheit = h 32 



Degrees Centigrade 



5 x (degrees F. - 32) 



PYROMETRY AND PYROMETERS 235 

Three other useful tables are also given on the following pages. 

Table 34. — Weight of Round, Octagon and Squake Carbon Tool 

Steel per Foot 



Size 








Size 








in 


Round 


Octagon 


Square 


in 


Round 


Octagon 


Square 


inches 








inches 








He 


0.010 


0.011 


0.013 


2M 


16.79 


17.71 


21.37 


X 


0.042 


0.044 


0.053 


2% 


18.51 


19.52 


23.56 


Ms 


0.094 


0.099 


0.120 


2H 


20.31 


21.42 


25.86 


X 


0.168 


0.177 


0.214 


2% 


22.20 


23.41 


28.27 


5 /U 


0.262 


0.277 


0.334 


3 


24.17 


25.50 


30.78 


X 


0.378 


0.398 


0.481 


ZX 


26.23 


27.66 


33.40 


Ke 


0.514 


0.542 


0.655 


ZX 


28.37 


29.92 


36.12 


X 


0.671 


0.708 


0.855 


3% 


30.59 


32.27 


38.95 


Kg 


0.850 


0.896 


1.082 


ZX 


32.90 


34.70 


41.89 


Vs 


1.049 


1.107 


1.336 


z% 


35.29 


37.23 


44.94 


%. 


1.270 


1.339 


1.616 


m 


37.77 


39.84 


48.09 


% 


1.511 


1.594 


1.924 


ZX 


40.33 


42.54 


51.35 


13 /l6 


1.773 


1.870 


2.258 


4 


42.97 


45.34 


54.72 


X 


2.056 


2.169 


2.618 


4M 


48.51 


51.17 


61.77 


15 /lG 


2.361 


2.490 


3.006 


±X 


54.39 


57.37 


69.25 


1 


2.686 


2.833 


3.420 


4% 


60.60 


63.92 


77.16 


M 


3.399 


3.585 


4.328 


5 


67.15 


70.83 


85.50 


IK 


4.197 


4.427 


5.344 


5X 


74.03 


78.08 


94.26 


i% 


5.078 


5.356 


6.646 


5X 


81.25 


85.70 


103.45 


IX 


6.044 


6.374 


7.695 


5% 


88.80 


93.67 


113.07 


l« 


7.093 


7.481 


9.031 


6 


96.69 


101.99 


123.12 


1M 


8.226 


8.674 


10.474 


7 


131.61 


138.82 


167.58 


i% 


9.443 


9.960 


12.023 


8 


171.90 


181.32 


218.88 


2 


10.744 


11.332 


13.680 


9 


217.57 


229.48 


277.02 


2M 


12.129 


12.793 


15.443 


10 


268.60 


283.31 


342.00 


2K 


13.598 


14.343 


17.314 


11 


325.01 


342.80 


413.82 


2% 


15.151 


15.981 


19.291 


12 


386.79 


407.97 


492.48 



High-speed steel, being more dense than carbon steel, weighs from 10 to 
11 per cent more than carbon steel. This should be added to figures given 
in the table. 



236 



THE WORKING OF STEEL 



Table 35. — Weight of Round, Carbon Tool Steel 12 In. in Diameter 
and Larger, per Foot 



Diameter, 


Weight 


Diameter, 


Weight 


Diameter, 


Weight 


inches 


per foot 


inches 


per foot 


inches 


per foot 


12 


386.790 


15% 


677.527 


19% 


.1,049.010 


12% 


395.518 


16 


687.600 


19% 


1,061.705 


12% 


404.246 


16% 


699.017 


20 


1,074.400 


12% 


412.974 


16% 


710.435 


20% 


1,088.502 


12% 


421 . 702 


16% 


721.852 


20% 


1,102.605 


12% 


430.430 


16% 


733.270 


20% 


1,116.707 


12% 


439.158 


16% 


744.687 


20% 


1,130.810 


12% 


447.886 


16% 


756.105 


20% 


1,144.912 


13 


456.615 


16% 


767.522 


20% 


1,159.015 


13% 


465.343 


17 


778.940 


20*% 


1,173.118 


13% 


474.071 


17% 


790.358 


21 


1,187.220 


13% 


482.799 


17% 


801 . 777 


21% 


1,201.322 


13% 


491.527 


17% 


813.195 


21% 


1,215.425 


13% 


500.255 


17% 


824.614 


21% 


1,229.527 


13% 


508 . 983 


17% 


836.030 


21% 


1,243.630 


13% 


517.711 


. 17% 


847.447 


21% 


1,257.732 


14 


526.440 


17% 


858.863 


21% 


1,271.835 


14% 


536.512 


18 


870.280 


21% 


1,285.937 


14% 


546.585 


18% 


883.105 


22 


1,300.040 


14% 


556.657 


18% 


895.920 


22% 


1,315.485 


14% 


566.730 


18% 


908.740 


22% 


1,330. 930 


14% 


576.802 


18% 


921.560 


22% 


1,346.375 


14% 


586.875 


18% 


934.380 


22% 


1,361.820 


14% 


596 . 947 


18% 


947.200 


22% 


1,377.265 


15 


607.020 


18% 


960.020 


22% 


1,392.710 


15% 


617.092 


19 


972.840 


22% 


1,408.155 


15% 


627.165 


19% 


985.035 


23 


1,423.600 


15% 


637.237 


19% 


998.230 


23% 


1,454.490 


15% 


647.310 


19% 


1010.925 


23% 


1,485.380 


15% 


657.382 


19% 


1,023.620 


23% 


1,516.270 


15% 


667.455 


19% 


1,036.315 


24 


1,547.160 



To find the weight of discs made of carbon steel, in diameters 
up to and including 12 in., without any allowance for finishing 
multiply the per foot weight of round bar steel, shown herewith 
by the decimal equivalent of a foot given in the following table : 



PYROMETRY AND PYROMETERS 237 

Table 36. — Decimal Equivalents of a Foot 



In. 





H 


H 


% 


V2 


Vs 


H 


Vs 





0.000 


0.010 


0.021 


0.031 


0.042 


0.052 


0.063 


0.073 


1 


0.083 


0.094 


0.104 


0.115 


0.125 


0.135 


0.146 


0.156 


2 


0.167 


0.177 


0.188 


0.198 


0.208 


0.219 


0.229 


0.240 


3 


0.250 


0.260 


0.270 


0.281 


0.292 


0.302 


0.313 


0.323 


4 


0.333 


0.344 


0.354 


0.364 


0.375 


0.385 


0.396 


0.406 


5 


0.416 


0.427 


0.437 


0.448 


0.458 


0.469 


0.479 


0.480 


6 


0.500 


0.510 


0.520 


0.531 


0.542 


0.552 


0.563 


0.573 


7 


0.583 


0.594 


0.604 


0.615 


0.625 


0.635 


0.646 


0.656 


8 


0.666 


0.677 


0.687 


0.698 


0.708 


0.719 


0.729 


0.740 


9 


0.750 


0.760 


0.770 


0.781 


0.792 


0.802 


0.813 


0.823 


10 


J3.833 


0.844 


0.854 


0.865 


0.875 


0.885 


0.896 


0.906 


11 


0.916 


0.927 


0.937 


0.948 


0.953 


0.969 


0.979 


0.990 



Example. — If the weight of a carbon steel disc 7 in. diameter, \% in. 
thick is desired, turn to page 233, where the per foot weight of 7 in. round is 
given as 131.6 lb. Multiply this by the decimal equivalent of 1% in., or 
0.135, as shown in the above table, and the product will be the net weight 
of the disc. 

131.61 lb. = the weight of 1 ft. of 7 in. round. 
0. 135 = the per foot decimal equivalent of 1% in. 



65805 
39483 
13161 



17.76735 lb. = weight of disc 7 in. diam. 1% in. thick without any 
allowance for finishing. 



238 



THE WORKING OF STEEL 
AUTHORITIES QUOTED 



Addis, W. H., 102 

American Machinists' Handbook, 
69 

American Steel Treaters' Soci- 
ety, 117 

American Gear Mfrs. Asso., Ill 

Automatic and Electric Fur- 
naces Ltd., 161 

Arnold, Prof. J. O., 167 

B 

Burleigh, R. W. 

Borden, B. 

Boker, Herman & Co. 

Brown Instrument Co., 224 

Brown, Lipe Chapin Co., 121 

C 
Campbell 

Curtis Airplane Co. 
Carhart, H. A., 42 

E 

Englehard, Charles, 227 
Ens aw, Howard, 12, 79, 95 

F 
Firth-Sterling Steel Co., 176 
Firth, Thomas & Sons, 137 
Fowler, Henry, 151 

G 
Gilbert & Barker, 164, 188 

H 
Hayward, C. R., 35 
Howe, Dr. H. M., 8* 
Hoover Steel Ball Co., 61 
Heathcote, H. L., 85 
Harris, Matthew, 94 
Hunter, J. V., 192 

J 

Janitzky, E. J., 117 



Latrobe Steel Co., 150, 178 
Ludlum Steel Co., 175 
Leeds & Northrup Co., 211 
Lyman, W. H., 199 

M 

Mansfield, C. A. 
Midvale Steel Co. 
McKenna, Roy C, 164 
Moulton, Seth A., 199 

N 
Niles, Bennet, Pond, 67 



Parker, S. W. 
Poole, C. R. 

S 

S. A. E. (Society Automatic En- 
gineers), 39, 46, 49, 134 
Sauveur, Albert, 105, 232 
Springfield Armory, 78, 120 
Sellack, T. G. 
Smith, A. J., 101 
Suverkrop, E. A., 121 
Shirley, Alfred J. 



Taylor Instrument Co., 215 

U 

U. S. Ball Bearing Co. 
United Steel Co. 
Underwood, Charles N. 

V 

Van Deventer, John H., 86 
W 



Johnston, A. B., 35 

Juthe, K. A., 1, 24, 65, 75, 79, 105, Wood, Harold F., 46 

145 Wheelock, Lovejoy & Co., 69 



INDEX 



A B C of iron and steel, ix 
Absorption of carbon, rate of, 83 
Air hardening steels, 183 
Analysis of high speed steel, 165 
Alloy steel, annealing, 76 

properties of, 34 
Alloys and their effect, 24 

in high speed steel, 166 

in steel, value of, 14 

upon steel, 24 
Alpha iron, 22, 105 
Annealing, 22 

care in, 154, 155 

furnace, 190 

high-chromium steel, 36 

high speed tools, 174 

in bone, 77 

methods, 122 

proper, 114 

rifle components, 78 

rust-proof steel, 36 

steels, 75 

temperature, 114 

work, 112 
Austentite, 22, 106 
Automotive industry, application of 
Liberty engine materials 
to, 46 

temperature control, 225 
Axles, heat treatment of, 61 



B 



Balls, making steel, 61 
Barium chloride process, 178 
Baths for tempering, 157 
Bessemer converter, 2 
Beta iron, 22, 105 
Blending compounds, 103 
Blue brittleness, 56 



Borax and sand as a flux, x 

Bone, annealing in, 77 

Boxes for case hardening or carburiz- 

ing, 80 
Breaking test gears, 126 
Brinell hardness, 13-19 

hardness and tensile, 20 

test, 116 
Broach hardening furnace, 188 
Brown automatic pyrometer, 224 
Burning, 23 



Calescence, 108 
Calorized tubes, 229 
Carbon, 107 

content at various tempera- 
tures, 84 

content of case hardened work, 
81 

in cast iron, ix 

in tool steel, 149-150 

introduction of, 96 

penetration of, 95 

steel, 15 

steel forgings, Liberty engine, 48 

steel tools, 145 

steels, S. A. E., 39 

steels, temper colors, 163 

tool steel, forging, 65 
Carbonizing, see Carburizing. 
Carborundum tubes, 229 
Carburization, preventing, 93 
Carburizing by gas, 93 

boxes, 80 

compounds, 102 

effect of size, 117 

gas consumption by, 101 

local, 94 

material, 85 

nickel steel, 125 

or case hardening, 79 
239 



240 



INDEX 



Carburizing by gas, pots for, 123 

process of, 113 

short method, 124 

sleeves, 132 
Car door type of furnace, 190 
Case hardening boxes, 80 

cast iron, 89 

local, 94 

or surface carburizing, 79 

see Carburizing, 
Case-hardening steels, 16 

treatments for various steels, 92 
Cast iron, carbon in, ix 

case hardening, 89 
Case, depth of, 86 
"Cementite," 21, 106 
Center column furnace, 186 
Centigrade table, 232-234 
Chamotte tubes, 228 
Chart of carbon penetration, 97 

and punches, steel for, 151 

heat treatment, 151 

shape, 151 
Chrome steel, 26-27 
Chrome-nickel steel, 27-28 

steel, forging, 66 
Chrome-vanadium steel, 15 
Chromium, 26-27, 107 

steels, S. A. E., 41 
Chromium-cobalt steel, 178 
Chromium-vanadium steel, S. A. E., 

41 
Classification of steel, 11 
. Clay tubes, 229 
Cold end compensator, 213 

junction errors, 222 

shortness, 166 

worked steel, 65 
Color in tempering, 157 
Colors on carbon steels, 163 
Combination tank, 90 
Comparison of fuels, 191 
Compensating leads, 222 
Compensator for cold ends, 214 

automatic, 214 
Composition of steel, 12, 105 
Compound, blending, 103 

separating from work, 102 
Compounds for carburizing, 102 



Connecting rods, Liberty motor, 
42, 52 

Continuous heating furnace, 71 

Controlling factors, 107 

Converter, bessemer, 2 

Cooling quenching oil, roof system, 
74 
rate of for gear-forgings, 51 

Copper, effect of in medium carbon 
steel, 35 

Copper-plating to prevent carburiz- 
ing, 93 

Corrosion of high-chromium steel, 38 
of rust-proof steel, 38 

Corundite tubes, 229 

Cost of operating furnaces, 200 

Cracks in hardening, preventing, 160 

Crankshaft, Liberty motor, 54 

Critical point, 112 
points, 10, 108 

Crucible or tool steel, annealing, 76 

Cutting off high speed steel, 172 

Cyanide bath for tool steel, 133 

D 

Decalescent point, 11-112 
Decarbonizing of outer surface, 153 

preventing, 154 
Depth of case, 86 
Detrimental elements in steel, 166 
Dies, drop forging, 133 

quenching, 147 

soft spots in, 147 

tempering round, 161 
Drawing, 23 

ends of gear teeth, 127 
Drop forging dies, 133 



E 



Effect of alloys, 167 

of different carburizing ma- 
terial, 87 
of size of piece, 89-117 
of copper in medium 
carbon steel, 35 
Electric process of steel making, 4 
Elements, different, 107 



INDEX 



241 



Enlarging steel, 161 
Equipment for heat treating, 121 
"Eutectic," 21 
"Eutectoid,"22 



Furnaces, tool, 187 

water cooled fronts, 197 
Fuels, comparison of, 191 

for furnaces, 199 



F 



Fahrenheit temperature table, 232- 

234 
"Ferrite," 21, 106 
Fish oil for hardening, 110 
Flame shields, 193 
Flange shields for furnaces, 197 
Flux, borax and sand, x 
Forging furnace, 189 

high speed tools, 174 

improper, 66 

of steel, 64 

practice, heavy, 195 

rifle barrels, 69 
Forgings, carbon steel Liberty 

engine, 48 
Formed tools, high speed, 174 
Fractures, examining by, 159 
Furnace, continuous heating, 71 

crucible, 4 

data, 199 

electric, 6 

Heroult, 6 

open hearth, 3 

records, 129 
Furnaces, 185 

annealing, 190 

broach hardening, 188 

car door type, 190 

center column, 186 

cost of operating, 200 

data on, 199 

forging, heavy, 195 

fuels for, 199 

gas fired, 190 

high speed steel, 187 

lead pot, 185 

manganese steel, 198 

muffle, 189 

oil fired, 186 

operating costs, 200 

screens for, 192 
16 



G 



Gages, changes due to quenching, 
162 

tempering, 161 
Gamma iron, 22, 105 
Gas, carburizing by, 93 

consumption for carburizing, 
101 

fired furnace, 190 

illumination for carburizing, 97 
Gear blanks, heat treatment of, 111 

forgings, rate of cooling for 
Liberty engine, 51 

hardening machine, 130 

steel, transmission, 59 

teeth, drawing ends of, 127 
Gears, Liberty engine, 50 
Gleason tempering machine, 129 
Grain, refining, 91 

size, 23 
Graphitic carbon, ix 
Grinding high speed steel, 176 



II 



Hair lines in forgings, 56 
Hardening carbon steel for tools, 145 
cracks, preventing, 160 
dies, 146 
gears, 130 

high speed steel, 171 
high speed tools, 177 
of high-chromium steel, 37 
of rust-proof steel, 37 J 
room, modern, 146 
Heating, effect of size, 117 
Heat, judging by color, 110 
treating departments, 122 
equipment, 121 
forgings, 44 
inspection of, 125 
Liberty motor, 44 
nickel chrome steel, 13 



242 



INDEX 



Heat, of axles, 61 
of chisels, 151 
of gears, 131 
of high speed steel, 170 
of rifle parts, 120 
of steel, 105 
S. A. E., 134-137 
treating, departments, treat- 
ment, difference in, 14 
Heroult furnace, 6 
High-chromium steel, 36 
annealing of, 36 
corrosion of, 38 
hardening of, 37 
Highly stressed parts of Liberty 

engine, 49 
High speed steel, analysis of, 166 
annealing, 75 
cutting off, 172 
forging, 65 
furnace, 187 
hardening, 171 
heat treatment of, 170 
instructions for, 175, 180 
manufacture, 166, 169 
pack hardening, 172 
structure of, 168 
Hints for steel users, 159 
"Hypo-eutectic,"21 
"Hypo-eutectoid,"22 



Illuminating gas for carburizing, 97 
Improper forging, 66 
Influence of size on heating, 117 
Inspection of heat treatment, 125 
Internal stresses, relieving, 154 
Introduction of carbon, 96 



Jewelers' tools, 146 

Judging heat of steel by color, 110 



Lathe and planer tools, 176 

tools, high speed, 173 
Latrobe temper list, 150 



Lead bath, 154 

pot furnace, 185 
Leeds & Northrup potentiometer, 
211 
optical pyrometer, 220 
Liberty engine, highly stressed parts 

of, 49 
Liberty engine materials, application 
to automatic industry, 46 
motor connecting rods, 42, 52 
motor, crankshaft, 54 
motor piston pin, 57 
Linseed oil for hardening, 110 
Local case hardening, 94 
Luting mixture, 100 

M 

Machineability of steel, 72 
Machinery steel, annealing, 77 
Magnet test, 109 
Malleable iron, ix 
Manganese, 29-30, 107 
steel, 15, 29-30 
furnace, 198 
Manufacture of high speed steel, 169 
Marquardt mass tubes, 228 
Martensite, 22, 106 
Medium carbon steel, effect of 

copper on, 35 
Microphotographs, 114 
Microscopic examination, 158 
Milling cutters, high speed, 174 
Mixture for luting, 100 
Modern hardening room, 146 
Molten metal pyrometers, 226 
Molybdenum, 32 
Muffle furnace, 189 

N 

Nickel, 107 

Nickel-chrome steel, 15-19 
Nickel-chromium, 27-28 
steels, S. A. E., 40 
Nickel, influence of on steel, 25 
steel, 24-26 

affinity for carbon, 125 
steels, 18 
S. A. E., 39 



INDEX 



243 



Non-homogeneous melting, 24 
Non-shrinking steels, 35 
"Normalizing," 22 
temperature, 16 



O 



Oil bath for tempering, 157 

cooling on roof, 74 

fired furnace, .186 

for hardening, 110 

hardening steel, forging, 66 
steels, 35 

temperature of quenching, 124 
Open hearth furnace, 3 
Operating costs of furnaces, 200 
Osmondite, 106 

Outer surface decarbonizer, 153 
Over-heated steel, restoring, 137 
Overheating, 23 

dies, 148 



Pack-hardening, 87 

high speed steel, 173 
Packing work for carburizing, 123 
Paste for hardening dies, 146 
"Pearlite,"21, 106 
Penetration of carbon, 95 
carbon, chart of, 97 
in case hardening, 83 
Phosphorous, 33 

Pickling Liberty motor forgings, 44 
Piston pin, Liberty motor, 57 
Placing pyrometers, 210 
Planer tools, high speed, 173 
"Points" of carbon in steel, 9 
Potentiometer, Leeds & Northrup, 

211 
Pots for carburizing, 123 
Press for testing gears, 126 
Preventing carburization, 93 

cracks in hardening, 160 
Properties of alloy steels, 34 

of alloy steels, table, 34 

of steel, 12 
Protective screens for furnaces, 192 
Puddled iron, ix 



Punches and chisels, steels for, 

151 
Py-rod, 208 
Pyrometers, 202 

calibration, 208 

copper ball, 202 

indicating, 219 

inspection, 208 

iron ball, 202 

molten metal, 226 

optical, 206, 220 

placing, 210 

recording, 216 

Siemens, 202 

testing, 209 

water, 203 



Q 



Quality and structure of high speed 
steel, 168 

of steel, 149 
Quenching, 22 

after carburizing, 86-88 

dies in tank, 147 

obsolete method, 148 

oil, temperature of, 124 

tank, 89 

tool steel, 156 



K 



Rate of absorption of carbon, 83 
Recalescence, 109 
Recalescent point, 11 
Recording temperatures, 127 
Red shortness, 166 
Refining the grain, 91 
Regenerative open hearth furnace, 3 
Restoring overheated steel, 137 
Rifle barrels, forging, 69 

components, annealing, 78 

parts, heat treatment of, 120 
Roof system of cooling oil, 74 
Rust-proof steel, 36 

annealing of, 36 

corrosion of, 38 

hardening of, 37 



244 



INDEX 



S 

S. A. E. carbon steels, 39 

chromium steels, 41 

chromium-vanadium, 41 

heat treatments, 134-137 

nickel-chromium steels, 40 

nickel steels, 39 

screw stock, 39 

silico-manganese steel, 41 

standard steels, 39 
Salt bath for tempering, 157 
Sclerescope test, 116 
Screens for furnaces, 192 
Screw stack, S. A. E., 39 
Sentinels, melting of, 207 
Separating work from compound, 

102 
Silversmiths' tools, 146 
Size of piece, effect of, 89-117 

influence of. 117 
Sleeves, carburizing, 132 

hardening and shrinking, 132 

shrinking, 132 
Shields for furnace doors, 193 
Short method of carburizing, 124 
Shrinking steel, 161 
Silica tubes, 228 
Silico-manganese steels, S. A. E., 

41 
Silicon, 33, 107 
Sorbite, 22, 106 
Specimens, test, 23 
Standard S. A. E. steels, 39 
Steel balls, stock for, 62 

bolts, making, 61 

composition of, 105 

for chisels and punches, 151 

forging of, 64 

give it a chance, 148 

heat treatment of, 105 

high speed, 165 

making, 1 

bessemer process, 1 
crucible process, 4 
electric furnace process, 4 
open hearth, 1 

tools, carbon, in, 149 

users' hints, 159 



Structure of high speed steel, 168 
Sulphur, 33, 108 



Tables, air, oil and water hardened 
steel, 38 

alloy steels, properties of, 34 

carbon content, 84 

carbon steels, 39 

case hardening, 97 

changes due to quenching, 162 

chromium steels, 41 

chromium-vanadium steels, 41 

colors and temperature, 163 

composition of steels, 51, 52 

cost of furnaces, 200 

effect of size, 118 

fuels, comparison of, 191 

high-chromium steel, 37 

nickel-chromium steels, 40 

nickel steels, 39 

operating cost of furnaces, 200 

production cost of furnaces, 
201 

S. A. E. steels, 49 

screw stock, 39 

silico-manganese steels, 41 

stock for balls, 62 

temperature conversion, 232- 
234 

tempering temperatures, 158 

weight of steel, 235-237 
Tank for quenching, 89 

dies, 147 
Taylor instruments, 215 
Temper, colors of, 157 

list, Latrobe, 150 

of steel, 149 
Temperature recorders, 127 

tables, 232-234 
Temperatures for tempering, 158 
Tempering colors on carbon steels, 
163 

gages, 161 

high speed tools, 177 

machine, Gleason, 129 

round dies, 161 

temperatures, 158 

theory of, 156 



INDEX 



245 



Tempers of carbon steel, 150 
Testing heat treatment, 125 
Tests of steel, 16 
Test specimens, 23 
Theory of tempering, 150 
Thermocouple, 204 

base metal, 205 

cold end, 206 

placing, 218 

protectors, 227 

rare metal, 205 
Time for hardening, take, 148 
Tool furnace, small, 187 

or crucible steel, annealing, 76 

steel, cyanide bath for, 133 
quenching, 150 
Tools, carbon in different, 149 

carbon steel, 145 

of high speed steel, 173 

tempers of various, 150 
Transmission gear steel, 59 
Treatments for various steels, 92 
Troosite, 22, 106 
Tubes, calorized, 229 

carborundum, 229 



Tubes, Chamotte, 22S 

clay, 229 

Marquardt mass, 22S 

silica, 228 
Tungsten, 30-32, 108 

steel, 30-32 

U 

Users of steel, hints for, 159 

V 

Vanadium, 28-29, 108 
steel, 28-29 

W 

Water annealing, 155 

cooled furnace fronts, 197 
Weight of steel bars, 235-237 
Working instructions for high speed 

steel, 175 
Wrought iron, ix 



